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The effect of follicular phase length on pregnancy outcomes and endometrial development in gonadotropin ovarian stimulation/intrauterine insemination (OS/IUI) cycles Jennifer B. Bakkensen MD , Georgios Christou MD , Irene Dimitriadis MD , Kaitlyn James PhD , Irene Souter MD PII: DOI: Reference:
S1472-6483(19)30851-X https://doi.org/10.1016/j.rbmo.2019.12.007 RBMO 2315
To appear in:
Reproductive BioMedicine Online
Received date: Revised date: Accepted date:
22 April 2019 3 December 2019 8 December 2019
Please cite this article as: Jennifer B. Bakkensen MD , Georgios Christou MD , Irene Dimitriadis MD , Kaitlyn James PhD , Irene Souter MD , The effect of follicular phase length on pregnancy outcomes and endometrial development in gonadotropin ovarian stimulation/intrauterine insemination (OS/IUI) cycles, Reproductive BioMedicine Online (2019), doi: https://doi.org/10.1016/j.rbmo.2019.12.007
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo editing, typesetting, and review of the resulting proof before it is published in its final form. Please note that during this process changes will be made and errors may be discovered which could affect the content. Correspondence or other submissions concerning this article should await its publication online as a corrected proof or following inclusion in an issue of the journal. © 2019 Published by Elsevier Ltd on behalf of Reproductive Healthcare Ltd.
Title: The effect of follicular phase length on pregnancy outcomes and endometrial development in gonadotropin ovarian stimulation/intrauterine insemination (OS/IUI) cycles
Authors’ names and affiliations: Jennifer B. Bakkensen, MD1 [email protected] Georgios Christou, MD1 [email protected] Irene Dimitriadis, MD1 [email protected] Kaitlyn James, PhD1 [email protected] Irene Souter, MD1 [email protected] 1
Massachusetts General Hospital Fertility Center, Department of Obstetrics and Gynecology,
Harvard Medical School, Boston, MA, USA
Postal address: Department of Obstetrics and Gynecology Massachusetts General Hospital 55 Fruit Street Boston, MA 02114
Corresponding author: Jennifer B. Bakkensen, MD Phone: 716-698-3570 Email: [email protected]
Abstract Research question: Does a shorter follicular phase length (FPL) affect pregnancy outcomes and endometrial development among women undergoing gonadotropin ovarian stimulation/intrauterine insemination (OS/IUI)?
Design: Retrospective cohort study of 4773 OS/IUI cycles among 2054 patients. FPL was analyzed first continuously, then dichotomously using an arbitrary cutoff at the 15th percentile (8 days) to divide cycles into shorter and longer FPL groups. ROC curves were constructed to further analyze the impact of FPL on all outcomes.
Primary outcomes included clinical pregnancy, spontaneous abortion, multiple pregnancy, and non-viable (ectopic/biochemical) pregnancy rates (CPR, SABR, MPR, and NVPR, respectively). Secondary outcomes included endometrial thickness (ET). All analyses controlled for age, day 3 FSH, and BMI.
Results: When analyzing FPL continuously, CPR increased by 6.0% (aOR 1.06, 95%CI: 1.031.09%, p<0.001) with each additional follicular phase day. Similarly, in the dichotomous analysis, cycles with a longer FPL resulted in higher CPR with 45% higher odds of clinical pregnancy (aOR 1.45, 95%CI: 1.07-1.97, p = 0.018). No effect of FPL was noted on NVPR, SABR, or MPR.
ET increased by 0.09 mm (95% CI: 0.06-0.12, p<0.001) with each additional FPL day and was increased in the longer compared to the shorter FPL group (adjusted mean difference 1.08mm, 95% CI: 0.81-1.34, p<0.001).
Conclusions: Our data suggest that in gonadotropin OS/IUI cycles, FPL might impact both chance of clinical pregnancy and ET, independent of maternal age and ovarian reserve.
Key words: Follicular phase length; ovarian stimulation; intrauterine insemination; endometrial thickness
Key Message: This large-scale retrospective study suggests a possible relationship, independent of age and ovarian reserve, between follicular phase length, endometrial thickness, and clinical pregnancy rates specifically among women undergoing gonadotropin-induced OS/IUI, an important first-line infertility treatment. These findings may help physicians in counseling their patients on the likelihood of successful OS/IUI treatment.
Introduction
Variation in length of the follicular phase, both among normally menstruating women and throughout a woman’s reproductive life, has been well-documented (Lenton et al., 1984; Sherman and Korenman, 1975; Treloar et al., 1967). Shortening of the follicular phase is thought to be related to early follicular recruitment during the luteal-follicular transition and advanced selection of the dominant follicle, resulting in earlier ovulation (Klein et al., 2002; Van Zonneveld et al., 2003).
Previous studies have suggested that among women with infertility, a shorter follicular phase occurring in association with early ovulation is associated with poor pregnancy outcomes compared to a longer follicular phase (Check et al., 2003, 1992; Khalil et al., 2001). While these studies were small and did not control for important confounders such as ovarian reserve, the
authors postulated that a shorter follicular phase may not allow sufficient time for full follicular maturation or may lead to inadequate development of the endometrial environment. Although plausible that a similar effect would be seen among women undergoing ovarian stimulation, the limited literature addressing the impact of a shorter duration of gonadotropin stimulation has not demonstrated similar adverse pregnancy outcomes (Alport et al., 2011; Mardešič et al., 2014; Martin et al., 2006). However, these studies have focused on women undergoing IVF and may not necessarily apply to women undergoing other, less aggressive, fertility treatments such ovarian stimulation (OS) with gonadotropins and intrauterine insemination (IUI). Further, the ovarian hyperstimulation central to IVF leads to supraphysiologic levels of estradiol (E2) not seen among IUI cycles which may mitigate the effects of a short follicular phase on the endometrium and clinical pregnancy, rendering conclusions from IVF studies non-applicable to the IUI population. As gonadotropin OS/IUI remains a widely practiced first-line treatment for infertile couples, it is important to understand how length of the follicular phase impacts cycle outcomes.
The goal of the present study was to evaluate the effect, if any, of a shorter follicular phase length (FPL) on pregnancy outcomes among infertile women undergoing gonadotropin OS/IUI. Specifically, the objective was to study the effect of a shorter FPL on: [1] the chance of achieving pregnancy, and [2] the thickness of the endometrium. We hypothesized that a shorter follicular phase would be associated with decreased chance of clinical pregnancy and decreased endometrial thickness (ET) at time of hCG trigger, even after controlling for potential confounders, such as age and ovarian reserve.
Materials and Methods
Study design The study protocol was approved by the Partners Healthcare Institutional Review Board. Data from patients undergoing a gonadotropin OS/IUI cycle at the Massachusetts General Hospital Fertility Center between December 1, 2003 and March 30, 2016 were retrospectively reviewed. The study cohort consisted of [1] women with a history of primary or secondary infertility and [2] single women or those in a same-sex relationship using donor sperm. A total of 4773 completed gonadotropin OS/IUI cycles from 2054 women were analyzed.
OS/IUI protocols At the time of treatment initiation, all women had completed a standard infertility work-up as previously described (Souter et al., 2011). All women had at least one patent fallopian tube documented by either hysterosalpingography or sonohysterosalpingography and all semen specimens had documented post-processing total motile sperm counts over 1,000,000.
Recombinant follicle stimulating hormone (rFSH) was started on cycle day 3 of a spontaneous or progesterone-induced menstrual bleed. The response to gonadotropins was monitored with serial ultrasound assessment and serum estradiol (E2) concentration with adjustments of the medication dose made as clinically indicated. Ovulation was triggered with recombinant human chorionic gonadotropin (rhCG) (Ovidrel, Serono Laboratories, Norwell, MA) when at least one follicle with a diameter 16 mm or greater was identified. Intrauterine insemination was performed 35-36 hours after the ovulation trigger. A quantitative serum β-hCG was drawn approximately 16 days thereafter unless spontaneous menses had occurred, with a serum β-hCG concentration of >6 mIU/ml constituting a positive pregnancy test. Clinical pregnancy was confirmed with a gestational sac on transvaginal ultrasound at approximately 4 weeks after insemination.
Cancelled cycles were excluded from the analysis. Reasons leading to cycle cancellation included overresponse (high number of pre-ovulatory follicles identified) or no response. A small percentage of cycles were cancelled due to non-medical reasons (e.g., for personal or social reasons).
Outcomes of interest FPL was measured from day 1 of menses to the day of hCG trigger.
Primary outcomes included clinical pregnancy, spontaneous abortion, multiple pregnancy, and non-viable (ectopic and biochemical) pregnancy rates (CPR, SABR, MPR, and NVPR, respectively). Clinical pregnancy was defined as the presence of one or more gestational sacs on ultrasound 4 weeks after insemination, with CPR expressed as the percentage of clinical pregnancies per completed OS/IUI cycles. SABR was defined as the percentage of clinical pregnancies aborted at less than 20 weeks’ gestational age and MPR was defined as the percentage of clinical pregnancies with two or more gestational sacs confirmed on ultrasound. Biochemical and ectopic pregnancies were considered non-viable pregnancies, with NVPR expressed as the percentage non-viable pregnancies per completed OS/IUI cycles. A secondary outcome of interest was ET (mm) on the day of hCG trigger, which was available for 2,017 of 4,773 cycles. Cycles with ET last checked before the day of hCG trigger (typically the day prior) were excluded from this analysis.
Statistical analysis Demographic factor comparisons between FPL groups were analyzed with Student t-tests, Mann Whitney U-tests, and χ2- tests, as appropriate. Multilevel random and fixed effects regression models were used to calculate odds ratios (ORs) for pregnancy outcomes and ET, with FPL analyzed first continuously, then by comparing FPL groups. An arbitrary cutoff at the
15th percentile of our population was selected to stratify cycles into a shorter FPL group (8 days) and a longer FPL group (>8 days).
All models adjusted for potential confounders including age, day 3 FSH, and BMI determined a priori as well as the effect of the same woman going through multiple cycles. Two sub-analyses were also performed. The first sub-analysis was limited to 2,017 of 4,773 cycles for which peak E2 was available on the day of hCG trigger such that cycles with peak E2 recorded before the day of hCG trigger (typically the day prior) were excluded. The second sub-analysis was limited to 3,911 cycles from women with ovulatory cycles, excluding cycles from women with diagnoses of polycystic ovarian syndrome or anovulation.
Finally, a ROC analysis was performed to determine whether a threshold FPL or ET existed for which clinical pregnancy varied significantly.
Results
Baseline patient demographics including age (years), BMI at cycle initiation (kg/m2), race, infertility diagnosis, day 3 FSH, gravidity, and parity are displayed in Table 1, stratified by FPL. As expected, women in the shorter FPL group were older with slightly higher (albeit within the normal range) day 3 FSH and higher incidence of idiopathic infertility and diminished ovarian reserve.
Table 2 summarizes the cycle characteristics for 4,773 completed gonadotropin OS/IUI cycles stratified by FPL. Among these cycles, FPL ranged from 6-38 days, with 729 cycles characterized by a shorter follicular phase (≤8 days) and 4044 characterized by a longer follicular phase (>8 days). While total gonadotropin dose was significantly different between the
two FPL groups (with a higher dose noted in the longer FPL group), response was similar between FPL groups, with similar peak E2. Number of follicles was also clinically similar between the two groups (median 2, interquartile range 1-2), albeit statistically different (p < 0.001). Notably, cycles with a longer follicular phase had increased ET as compared to cycles with a shorter follicular phase.
Results for pregnancy outcomes are summarized in Tables 3-4. All analyses adjusted for potential confounders including age, day 3 FSH, BMI, and the fact that some women underwent more than one cycle. When FPL was analyzed as a continuous variable, we found that the odds of clinical pregnancy increased by 6.0% with each additional day of the follicular phase (aOR 1.06, 95% CI 1.03-1.09, p < 0.001) (Table 3). When analyzing the FPL as a dichotomous variable, cycles with a longer compared to those with a shorter follicular phase resulted in significantly higher CPR (13.8 vs. 9.2%, p = 0.001). The adjusted odds for clinical pregnancy were 45% higher in the former compared to the latter group (aOR: 1.45, 95% CI: 1.07-1.97, p = 0.018). However, ROC analysis failed to identify a particular FPL cutoff that significantly impacted CPR (AUC = 0.57). FPL did not impact NVPR, SABR, or MPR in either analysis (Tables 3-4).
In order to account for a potential impact of follicular response on pregnancy outcomes, we performed a sub-analysis limited to the sub-group of 2,017 cycles for which serum peak E2 results were available on the day of hCG trigger. When pregnancy outcomes were analyzed including the effect of peak E2 in addition to the mixed effect of age, BMI, day 3 FSH, and woman in the adjusted models, the effect of FPL on pregnancy outcomes was in the same direction but attenuated, losing statistical significance for CPR in both the continuous analysis (aOR 1.03, 95% CI: 0.98-1.07, p = 0.262) and the dichotomous analysis (aOR 1.15, 95% CI: 0.69-1.88, p = 0.611) (Supplemental Table 3a and Table 4a).
Endometrial thickness was analyzed for this same subset of 2,017 cycles with ET available from day of hCG administration. Analysis of FPL as a continuous variable revealed that ET increased by 0.09 mm (95% CI: 0.06-0.12, p <0.001) with each additional day of the follicular phase. The adjusted mean difference between the longer and shorter follicular phase length groups was 1.08 mm (95% CI: 0.81-1.34, p < 0.001); however, an ROC analysis again failed to identify a specific FPL cutoff for which ET varied significantly (AUC = 0.5117).
A second sub-analysis limited to 3,911 cycles from women with ovulatory cycles was performed. When FPL was analyzed continuously, the association between FPL and clinical pregnancy was again attenuated (aOR 1.04, 95% CI 0.99-1.09) . However, in the dichotomous analysis, cycles characterized by a longer follicular phase had significantly higher CPR than cycles characterized by a shorter follicular phase (12.6% vs. 8.8%, p = 0.005) (Supplemental Table 3b and 4b). Additionally, median ET was significantly higher among cycles with a longer follicular phase (8.7mm, IQR 7.2mm-10mm) compared to those with a shorter follicular phase (7.3mm, IQR 6.3mm-8.7mm) (p <0.001).
Discussion
Gonadotropin OS/IUI is a commonly practiced first-line treatment for a wide range of infertility diagnoses. This study explored the effect of FPL on the outcome of gonadotropin OS/IUI cycles and found that a shorter follicular phase was associated with a decreased chance of clinical pregnancy, a finding that persisted even after adjustment for potential confounders including age and measures of ovarian reserve. The rates of non-viable pregnancy, spontaneous abortion, and multiple pregnancy were similar between FPL groups.
Consistent with prior studies of both natural and stimulated cycles (Lenton et al., 1984; Sherman and Korenman, 1975; Treloar et al., 1967), this study revealed variation in length of the follicular phase, with about 15 percent of women noted to have a shorter follicular phase of ≤8 days. Compared to women with a longer follicular phase, those with a shorter follicular phase tended to be older with a lower median BMI and a higher incidence of decreased ovarian reserve (as indicated by day 3 FSH levels) and idiopathic infertility, trends which have been previously welldocumented in the literature (Jukic et al., 2007; Kato et al., 1999; Lenton et al., 1984; Sherman and Korenman, 1975; Van Zonneveld et al., 2003) and for which our analyses were adjusted a priori. Despite these differences, the two FPL groups were comparable in the number of follicles produced per cycle (median two per cycle) and in peak E2 levels suggesting a similar response to stimulation after appropriate adjustments to the gonadotropin dose.
Our data suggest that among women undergoing gonadotropin OS/IUI cycles, even after controlling for the mixed effects of patients undergoing multiple cycles, age, BMI, and day 3 FSH, FPL may impact pregnancy outcomes. When FPL was analyzed as a continuous variable, CPR significantly increased with each day of the follicular phase, and when FPL was analyzed as a dichotomous variable (shorter vs. longer FPL), the results were similar, with a decreased chance of clinical pregnancy among women with a shorter FPL. However, ROC analysis failed to identify a critical FPL cutoff.
Our results support and strengthen the conclusions of previous studies on the effect of follicular phase length among women with infertility (Check et al., 2003, 1992; Khalil et al., 2001). Our study specifically adjusted for several important potential confounders, most notably markers of ovarian reserve, which were not accounted for in these earlier studies. Further, our study contained more than five times the number of cycles included in either of these previous studies. Our findings are, however, in contrast to more recent studies of women undergoing
ovarian stimulation for IVF cycles, which have not shown an effect of FPL on pregnancy outcomes (Alport et al., 2011; Mardešič et al., 2014; Martin et al., 2006). It is possible that women pursuing IUI represent a distinct patient population from those pursuing IVF, and that underlying differences between these two groups account for the differing impact of FPL. Alternatively, it could be that a difference in protocols accounts for the discrepant results. For example, the protocols used in two of the IVF studies involved administration of GnRH agonists starting from the mid-luteal phase of the previous cycle until the day of hCG trigger (Alport et al., 2011; Martin et al., 2006). Recent data suggests that use of GnRH agonists among infertile women with a shorter follicular phase may actually lengthen the follicular phase by about 3 days and partially restore fecundity (Cédrin-Durnerin et al., 2003), presumably by pituitary downregulation and inhibition of advanced follicular recruitment and development. The use of GnRH agonists may therefore mitigate the influence of FPL on cycle outcomes. Finally, and perhaps most importantly, the supraphysiologic levels of estrogens among women undergoing IVF may attenuate the negative effect on the endometrium induced by a shorter follicular phase. In contrast, peak E2 levels in OS/IUI cycles more closely resemble E2 levels in natural cycles, as demonstrated by the peak E2 levels in the present study. For these reasons, studies on follicular phase length pertaining specifically to patients undergoing ovarian stimulation for IVF are not applicable to patients undergoing stimulation for IUI, and the two should not be compared.
In regard to the effect of FPL on the endometrium, our data suggests that in cycles with a longer follicular phase, ET is increased. Numerous studies have correlated ET after ovarian stimulation with improved chance of conception during IVF (Gonen and Casper, 1990; Kovacs et al., 2003; Noyes et al., 1995; Richter et al., 2007), with most investigators agreeing that an ET of at least 6 mm is necessary for successful implantation (Gonen and Casper, 1990). Several recent studies suggest that ET is similarly correlated with increased chance of implantation and pregnancy during IUI cycles (Bromer et al., 2009; Esmailzadeh and Faramarzi, 2007; Maher et al., 2017;
Wolff et al., 2013). It is therefore possible that the effect of FPL on CPR may be partially attributable to increased time for endometrial development and potentially improved endometrial receptivity. While the difference in ET between those with a shorter versus longer FPL in our study was small and potentially clinically insignificant, the results highlight a biologically plausible mechanism that may partially explain the relationship between FPL and CPR.
Interestingly, in the sub-analysis limited only to those cycles with peak E2 levels available on day of hCG trigger, the noted differences persisted in the same direction but the effects were attenuated. This finding is suggestive of a possible impact of E2 on pregnancy outcomes, which is expected. However, given the FPL groups were similar in both median number of follicles and in median peak E2 levels, is seems unlikely that these variables would represent significant confounders. It is possible that the attenuated effect of FPL in the sub-analysis is a result of the smaller sample size, as more than half of patients last had E2 levels checked the day before rather than the day of hCG trigger and were therefore excluded from the subgroup. It is also worth noting that patients for whom E2 is measured on the day of hCG trigger in our practice tend to be those patients requiring closer monitoring during their cycle, including high responders and younger patients. It is therefore possible that the difference in magnitude of the FPL effect in the sub-analysis may in part be explained by underlying differences of the subgroup population rather than the effect of follicular response per se.
In the sub-analysis limited to women with ovulatory cycles, the relationship between FPL and CPR was also attenuated but persisted in the dichotomous analysis, with the longer FPL group demonstrating higher CPR and increased ET. The attenuation of the relationship between FPL and CPR in the continuous analysis after exclusion of patients with ovulatory disorders might be a reflection of this group’s more favorable prognosis with gonadotropin IUI (Mitwally and Casper, 2004). However, the persistence of the association in the dichotomous analysis (when
utilizing a cut-off identifying cycles with very short FPL) even after the exclusion of anovulatory cycles suggests that factors other than infertility diagnoses are responsible for the lower CPR observed in cycles with short FPL.
The data set reported in this study is one of the largest series to date of women undergoing gonadotropin OS/IUI. Patients with a wide range of demographic factors and infertility diagnoses were included, enhancing the generalizability of the data. The study is further strengthened by the uniformity of the protocol used, with all patients treated in one academic center with the same stimulation protocol using gonadotropins only. Finally, our study took into account and adjusted for the possible effect of both maternal age and diminished ovarian reserve on all outcomes.
The study has several notable limitations. First, clinical pregnancy was the primary outcome and not live birth because nearly 50% of the study population ultimately received their obstetrical care at outside facilities rendering delivery information difficult to obtain. While this is certainly a limitation of our study, clinical pregnancy remains a critically important outcome for reproductive endocrinologists that routinely discharge patients to OB care once viability is confirmed. Nevertheless, the relationship between FPL and clinical pregnancy remains of interest. Second, measures of ovarian reserve included day 3 FSH but not AMH levels. The main reason for this is the fact that this large database partially predates the now common practice of obtaining routine anti-Mullerian hormone (AMH) levels for ovarian reserve testing. As such, this variable was not included or adjusted for in our analyses. However, day 3 FSH remains a well-validated proxy for ovarian reserve and continues to be used to define and diagnose diminished ovarian reserve in clinical practice. Finally, the study is limited by its retrospective design. However, as it is not practical to randomize women to predetermined lengths of stimulation given the risks of
spontaneous ovulation or triggered ovulation of premature oocytes, retrospective studies of FPL among women undergoing gonadotropin OS/IUI have value.
In conclusion, our findings suggest that the duration of the follicular phase might be impacting certain outcomes of gonadotropin OS/IUI cycles, namely clinical pregnancy rates and endometrial thickness, although no critical FPL cutoff was identified. While a causal relationship cannot be established based on retrospective data, the reported association suggests that an ultra-short follicular phase may negatively impact the endometrial milieu, thereby impeding implantation and leading to lower clinical pregnancy rates. Further studies are necessary to determine whether manipulating FPL either by modifying hormonal stimulation protocols or adding GnRH agonists prior to cycle initiation could result in improved pregnancy rates in this population. Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
References
Alport, B., Case, A., Lim, H., Baerwald, A., 2011. Does the Ovarian Stimulation Phase Length Predict In vitro Fertilization Outcomes ? Int. J. Fertil. Steril. 5, 134–141. Bromer, J.G., Aldad, T.S., Taylor, H.S., 2009. Defining the proliferative phase endometrial defect. Fertil. Steril. 91, 698–704. https://doi.org/10.1016/j.fertnstert.2007.12.066 Cédrin-Durnerin, I., Bstandig, B., Galey, J., Bry-Gauillard, H., Massin, N., Hugues, J.N., 2003. Beneficial effects of GnRH agonist administration prior to ovarian stimulation for patients with a short follicular phase. Reprod. Biomed. Online 7, 179–184. https://doi.org/10.1016/S1472-6483(10)61748-8
Check, J., Adelson, H., Lurie, D., Jamison, T., 1992. Effect of the Short Follicular Phase on Subsequent Conception. Gynecol. Obstet. Investiation 34, 180–183. Check, J., Liss, J., Shucoski, M., 2003. Effect of short follicular phase with follicular maturity on conception outcome. Clin. Exp. Obstet. Gynecol. 30, 195–196. Esmailzadeh, S., Faramarzi, M., 2007. Endometrial thickness and pregnancy outcome after intrauterine insemination. Fertil. Steril. 88, 432–437. https://doi.org/10.1016/j.fertnstert.2006.12.010 Gonen, Y., Casper, R.F., 1990. Prediction of implantation by the sonographic appearance of the endometrium during controlled ovarian stimulation for in vitro fertilization (IVF). J. In Vitro Fert. Embryo Transf. 7, 146–152. https://doi.org/10.1007/BF01135678 Jukic, A.M.Z., Weinberg, C.R., Baird, D.D., Wilcox, A.J., 2007. Lifestyle and Reproductive Factors Associated with Follicular Phase Length. J. Women’s Heal. 16, 1340–1347. https://doi.org/10.1089/jwh.2007.0354 Kato, I., Toniolo, P., Koenig, K.L., Shore, R.E., Zeleniuch-Jacquotte, A., Akhmedkhanov, A., Riboli, E., 1999. Epidemiologic correlates with menstrual cycle length in middle aged women. Eur. J. Epidemiol. 15, 809–14. Khalil, M.R., Rasmussen, P.E., Erb, K., Laursen, S.B., Rex, S., Westergaard, L.G., 2001. Homologous intrauterine insemination. An evaluation of prognostic factors based on a review of 2473 cycles. Acta Obstet. Gynecol. Scand. 80, 74–74. https://doi.org/10.1080/791201839 Klein, N.A., Harper, A.J., Houmard, B.S., Sluss, P.M., Soules, M.R., 2002. Is the short follicular phase in older women secondary to advanced or accelerated dominant follicle development? J. Clin. Endocrinol. Metab. 87, 5746–5750. https://doi.org/10.1210/jc.2002020622 Kovacs, P., Matyas, S., Boda, K., Kaali, S.G., 2003. The effect of endometrial thickness on IVF/ICSI outcome. Hum. Reprod. 18, 2337–2341. https://doi.org/10.1093/humrep/deg461
Lenton, E.A., Landgren, B.-M., Sexton, L., Harper, R., 1984. Normal variation in the length of the follicular phase of the menstrual cycle: effect of chronological age. Br. J. Obstet. An Int. J. Obstet. Gynaecol. 91, 681–684. https://doi.org/10.1111/j.1471-0528.1984.tb04830.x Maher, M.A., Abdelaziz, A., Shehata, Y.A., 2017. Effect of follicular diameter at the time of ovulation triggering on pregnancy outcomes during intrauterine insemination. Int. J. Gynecol. Obstet. 139, 174–179. https://doi.org/10.1002/ijgo.12291 Mardešič, T., Mannaerts, B., Abuzeid, M., Levy, M., Witjes, H., Fauser, B.C.J.M., 2014. Short follicular phase of stimulation following corifollitropin alfa or daily recombinant FSH treatment does not compromise clinical outcome: A retrospective analysis of the Engage trial. Reprod. Biomed. Online 28, 462–468. https://doi.org/10.1016/j.rbmo.2013.12.009 Martin, J.R., Mahutte, N.G., Arici, A., Sakkas, D., 2006. Impact of duration and dose of gonadotrophins on IVF outcomes. Reprod. Biomed. Online 13, 645–650. https://doi.org/10.1016/S1472-6483(10)60654-2 Mitwally, M.F.M., Casper, R.F., 2004. Aromatase inhibition reduces the dose of gonadotropin required for controlled ovarian hyperstimulation. J. Soc. Gynecol. Investig. 11, 406–415. https://doi.org/10.1016/j.jsgi.2004.03.006 Noyes, N., Liu, H.C., Sultan, K., Schattman, G., Rosenwaks, Z., 1995. Implantation: Endometrial thickness appears to be a significant factor in embryo implantation in in-vitro fertilization. Hum. Reprod. 10, 919–922. https://doi.org/10.1093/oxfordjournals.humrep.a136061 Richter, K.S., Bugge, K.R., Bromer, J.G., Levy, M.J., 2007. Relationship between endometrial thickness and embryo implantation, based on 1,294 cycles of in vitro fertilization with transfer of two blastocyst-stage embryos. Fertil. Steril. 87, 53–59. https://doi.org/10.1016/j.fertnstert.2006.05.064 Sherman, B.M., Korenman, S.G., 1975. Hormonal characteristics of the human menstrual cycle throughout reproductive life. J. Clin. Invest. 55, 699–706. https://doi.org/10.1172/JCI107979
Souter, I., Baltagi, L.M., Kuleta, D., Meeker, J.D., Petrozza, J.C., 2011. Women, weight, and fertility: The effect of body mass index on the outcome of superovulation/intrauterine insemination cycles. Fertil. Steril. 95, 1042–1047. https://doi.org/10.1016/j.fertnstert.2010.11.062 Treloar, A.E., Boynton, R.E., Behn, B.G., Brown, B.W., 1967. Variation of the human menstrual cycle through reproductive life. Int. J. Fertil. Steril. 12, 77–126. https://doi.org/10.1097/00006254-196801000-00019 Van Zonneveld, P., Scheffer, G.J., Broekmans, F.J.M., Blankenstein, M.A., De Jong, F.H., Looman, C.W.N., Habbema, J.D.F., Te Velde, E.R., 2003. Do cycle disturbances explain the age-related decline of female fertility? Cycle characteristics of women aged over 40 years compared with a reference population of young women. Hum. Reprod. 18, 495–501. https://doi.org/10.1093/humrep/deg138 Wolff, E.F., Bahidi, N., Alford, C., Richter, K., Widra, E., 2013. Influences on endometrial development during intrauterine insemination: clinical experience of 2,929 patients with unexplained infertility. Fertil. Steril. 100, 194–9. https://doi.org/10.1021/nl061786n.CoreShell
Jennifer Bakkensen received her B.S. from the University of North Carolina at Chapel Hill and M.D. from Weill Cornell Medical College. She is a resident in the Brigham and Women’s and Massachusetts General Hospital Residency in Obstetrics and Gynecology and plans to pursue a fellowship in Reproductive Endocrinology and Infertility.
Key message
This large-scale retrospective study suggests a possible relationship, independent of age and ovarian reserve, between follicular phase length, endometrial thickness, and clinical pregnancy rates specifically among women undergoing gonadotropin-induced OS/IUI, an important firstline infertility treatment. These findings may help physicians in counseling their patients on the likelihood of successful OS/IUI treatment.
Table 1. Baseline demographic characteristics of 2,054 patients
Age, years BMI, kg/m2 Race/ethnic group Caucasian Non-Caucasian Day 3 FSH levels, IU/l Infertility Diagnosis Unexplained Male Factor Anovulation Polycystic ovarian syndrome Diminished ovarian reserve Tubal Factor Uterine Factor Endometriosis Combined Factors Other Prior Gravidity Prior Parity
Shorter follicular phase ≤8 days N = 311 (15%) 37 (34-40) 22.6 (20.8-24.8)
Longer follicular phase >8 days N=1743 (85%) 35 (32-38) 23.4 (21.1-26.8)
171 (55) 140 (45) 7.5 (6.4-9.8)
850 (49) 893 (51) 7 (5.7-8.8)
112 (36) 28 (9) 5 (2) 4 (1)
595 (34) 211 (12) 122 (7) 159 (9)
82 (26)
232 (13)
10 (3) 4 (1) 6 (2) 47 (15) 11 (5) 143 (46) 72 (23)
56 (3) 12 (<1) 43 (2) 269 (15) 43 (4) 821 (47) 423 (24)
All values expressed as n (%) or median (interquartile range) as appropriate.
p-value
<.001 <.001 .760
<.001 <.001
.695 .664
Table 2. Cycle characteristics of 4,773 Gonadotropin OS/IUI cycles
Follicular phase length, days Total Gn dose, IU Peak E2a, pg/mL No of Follicles ≥13mmb Endometrial Thicknessa, mm
Shorter follicular phase ≤8 days N = 728 (15%) 8 (8-8)
Longer follicular phase >8 days N = 4045 (85%) 11 (10-13)
p-value
375 (300-750) 302 (223-452) 2 (1-2)
675 (462.5-1050) 306 (196-468) 2 (1-2)
<.001 .523 <.001
7.7 (6.7-9)
9 (7.7-10.2)
<.001
<.001
All values expressed as median (interquartile range). Among women who had E2 and endometrial thickness recorded on the day of the trigger (N = 2,017). b Recorded on the last visit prior to or on the day of trigger. a
Table 3. Effect of follicular phase length as a continuous variable (days) on clinical pregnancy outcomes
Clinical pregnancy Non-viable pregnancy Spontaneous abortion Multiple pregnancy
OR (95% CI) associated with each additional day of follicular phase 1.06 (1.03, 1.09) 1.03 (0.96, 1.11) 1.06 (1.00, 1.13) .99 (0.92, 1.06)
All models controlled for age, BMI, day 3 FSH, and woman
p-value
<.001 0.376 0.049 0.767
Table 4. Effect of follicular phase length as a dichotomous variable (shorter vs. longer follicular phase) on clinical pregnancy outcomes
Shorter follicular phase ≤8 days N = 728 (15%) Clinical pregnancy Non-viable pregnancy Spontaneous abortion Multiple pregnancy a
67 (9.2)
Longer p-value follicular phase >8 days N = 4045 (85%) 558(13.8) .001
11 (1.5)
61 (1.5)
.999
12 (17.9)
107 (19.2)
.792
5 (7.5)
73 (13.1)
.186
aOR (95% CI) a p-value
1.45 (1.07, 1.97) .88 (.45, 1.72)
.018
1.32 (.67, 2.61) 1.83 (.70, 4.75)
.425
.701
.215
Odds ratios for longer follicular phase versus the referent shorter follicular phase controlling for the mixed effect of woman, age, BMI, and day 3 FSH.
The effect of follicular phase length on pregnancy outcomes and endometrial development in gonadotropin ovarian stimulation/intrauterine insemination (OS/IUI) cycles Jennifer B. Bakkensen MD , Georgios Christou MD , Irene Dimitriadis MD , Kaitlyn James PhD , Irene Souter MD PII: DOI: Reference:
S1472-6483(19)30851-X https://doi.org/10.1016/j.rbmo.2019.12.007 RBMO 2315
To appear in:
Reproductive BioMedicine Online
Received date: Revised date: Accepted date:
22 April 2019 3 December 2019 8 December 2019
Please cite this article as: Jennifer B. Bakkensen MD , Georgios Christou MD , Irene Dimitriadis MD , Kaitlyn James PhD , Irene Souter MD , The effect of follicular phase length on pregnancy outcomes and endometrial development in gonadotropin ovarian stimulation/intrauterine insemination (OS/IUI) cycles, Reproductive BioMedicine Online (2019), doi: https://doi.org/10.1016/j.rbmo.2019.12.007
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo editing, typesetting, and review of the resulting proof before it is published in its final form. Please note that during this process changes will be made and errors may be discovered which could affect the content. Correspondence or other submissions concerning this article should await its publication online as a corrected proof or following inclusion in an issue of the journal. © 2019 Published by Elsevier Ltd on behalf of Reproductive Healthcare Ltd.
Title: The effect of follicular phase length on pregnancy outcomes and endometrial development in gonadotropin ovarian stimulation/intrauterine insemination (OS/IUI) cycles
Authors’ names and affiliations: Jennifer B. Bakkensen, MD1 [email protected] Georgios Christou, MD1 [email protected] Irene Dimitriadis, MD1 [email protected] Kaitlyn James, PhD1 [email protected] Irene Souter, MD1 [email protected] 1
Massachusetts General Hospital Fertility Center, Department of Obstetrics and Gynecology,
Harvard Medical School, Boston, MA, USA
Postal address: Department of Obstetrics and Gynecology Massachusetts General Hospital 55 Fruit Street Boston, MA 02114
Corresponding author: Jennifer B. Bakkensen, MD Phone: 716-698-3570 Email: [email protected]
Abstract Research question: Does a shorter follicular phase length (FPL) affect pregnancy outcomes and endometrial development among women undergoing gonadotropin ovarian stimulation/intrauterine insemination (OS/IUI)?
Design: Retrospective cohort study of 4773 OS/IUI cycles among 2054 patients. FPL was analyzed first continuously, then dichotomously using an arbitrary cutoff at the 15th percentile (8 days) to divide cycles into shorter and longer FPL groups. ROC curves were constructed to further analyze the impact of FPL on all outcomes.
Primary outcomes included clinical pregnancy, spontaneous abortion, multiple pregnancy, and non-viable (ectopic/biochemical) pregnancy rates (CPR, SABR, MPR, and NVPR, respectively). Secondary outcomes included endometrial thickness (ET). All analyses controlled for age, day 3 FSH, and BMI.
Results: When analyzing FPL continuously, CPR increased by 6.0% (aOR 1.06, 95%CI: 1.031.09%, p<0.001) with each additional follicular phase day. Similarly, in the dichotomous analysis, cycles with a longer FPL resulted in higher CPR with 45% higher odds of clinical pregnancy (aOR 1.45, 95%CI: 1.07-1.97, p = 0.018). No effect of FPL was noted on NVPR, SABR, or MPR.
ET increased by 0.09 mm (95% CI: 0.06-0.12, p<0.001) with each additional FPL day and was increased in the longer compared to the shorter FPL group (adjusted mean difference 1.08mm, 95% CI: 0.81-1.34, p<0.001).
Conclusions: Our data suggest that in gonadotropin OS/IUI cycles, FPL might impact both chance of clinical pregnancy and ET, independent of maternal age and ovarian reserve.
Key words: Follicular phase length; ovarian stimulation; intrauterine insemination; endometrial thickness
Key Message: This large-scale retrospective study suggests a possible relationship, independent of age and ovarian reserve, between follicular phase length, endometrial thickness, and clinical pregnancy rates specifically among women undergoing gonadotropin-induced OS/IUI, an important first-line infertility treatment. These findings may help physicians in counseling their patients on the likelihood of successful OS/IUI treatment.
Introduction
Variation in length of the follicular phase, both among normally menstruating women and throughout a woman’s reproductive life, has been well-documented (Lenton et al., 1984; Sherman and Korenman, 1975; Treloar et al., 1967). Shortening of the follicular phase is thought to be related to early follicular recruitment during the luteal-follicular transition and advanced selection of the dominant follicle, resulting in earlier ovulation (Klein et al., 2002; Van Zonneveld et al., 2003).
Previous studies have suggested that among women with infertility, a shorter follicular phase occurring in association with early ovulation is associated with poor pregnancy outcomes compared to a longer follicular phase (Check et al., 2003, 1992; Khalil et al., 2001). While these studies were small and did not control for important confounders such as ovarian reserve, the
authors postulated that a shorter follicular phase may not allow sufficient time for full follicular maturation or may lead to inadequate development of the endometrial environment. Although plausible that a similar effect would be seen among women undergoing ovarian stimulation, the limited literature addressing the impact of a shorter duration of gonadotropin stimulation has not demonstrated similar adverse pregnancy outcomes (Alport et al., 2011; Mardešič et al., 2014; Martin et al., 2006). However, these studies have focused on women undergoing IVF and may not necessarily apply to women undergoing other, less aggressive, fertility treatments such ovarian stimulation (OS) with gonadotropins and intrauterine insemination (IUI). Further, the ovarian hyperstimulation central to IVF leads to supraphysiologic levels of estradiol (E2) not seen among IUI cycles which may mitigate the effects of a short follicular phase on the endometrium and clinical pregnancy, rendering conclusions from IVF studies non-applicable to the IUI population. As gonadotropin OS/IUI remains a widely practiced first-line treatment for infertile couples, it is important to understand how length of the follicular phase impacts cycle outcomes.
The goal of the present study was to evaluate the effect, if any, of a shorter follicular phase length (FPL) on pregnancy outcomes among infertile women undergoing gonadotropin OS/IUI. Specifically, the objective was to study the effect of a shorter FPL on: [1] the chance of achieving pregnancy, and [2] the thickness of the endometrium. We hypothesized that a shorter follicular phase would be associated with decreased chance of clinical pregnancy and decreased endometrial thickness (ET) at time of hCG trigger, even after controlling for potential confounders, such as age and ovarian reserve.
Materials and Methods
Study design The study protocol was approved by the Partners Healthcare Institutional Review Board. Data from patients undergoing a gonadotropin OS/IUI cycle at the Massachusetts General Hospital Fertility Center between December 1, 2003 and March 30, 2016 were retrospectively reviewed. The study cohort consisted of [1] women with a history of primary or secondary infertility and [2] single women or those in a same-sex relationship using donor sperm. A total of 4773 completed gonadotropin OS/IUI cycles from 2054 women were analyzed.
OS/IUI protocols At the time of treatment initiation, all women had completed a standard infertility work-up as previously described (Souter et al., 2011). All women had at least one patent fallopian tube documented by either hysterosalpingography or sonohysterosalpingography and all semen specimens had documented post-processing total motile sperm counts over 1,000,000.
Recombinant follicle stimulating hormone (rFSH) was started on cycle day 3 of a spontaneous or progesterone-induced menstrual bleed. The response to gonadotropins was monitored with serial ultrasound assessment and serum estradiol (E2) concentration with adjustments of the medication dose made as clinically indicated. Ovulation was triggered with recombinant human chorionic gonadotropin (rhCG) (Ovidrel, Serono Laboratories, Norwell, MA) when at least one follicle with a diameter 16 mm or greater was identified. Intrauterine insemination was performed 35-36 hours after the ovulation trigger. A quantitative serum β-hCG was drawn approximately 16 days thereafter unless spontaneous menses had occurred, with a serum β-hCG concentration of >6 mIU/ml constituting a positive pregnancy test. Clinical pregnancy was confirmed with a gestational sac on transvaginal ultrasound at approximately 4 weeks after insemination.
Cancelled cycles were excluded from the analysis. Reasons leading to cycle cancellation included overresponse (high number of pre-ovulatory follicles identified) or no response. A small percentage of cycles were cancelled due to non-medical reasons (e.g., for personal or social reasons).
Outcomes of interest FPL was measured from day 1 of menses to the day of hCG trigger.
Primary outcomes included clinical pregnancy, spontaneous abortion, multiple pregnancy, and non-viable (ectopic and biochemical) pregnancy rates (CPR, SABR, MPR, and NVPR, respectively). Clinical pregnancy was defined as the presence of one or more gestational sacs on ultrasound 4 weeks after insemination, with CPR expressed as the percentage of clinical pregnancies per completed OS/IUI cycles. SABR was defined as the percentage of clinical pregnancies aborted at less than 20 weeks’ gestational age and MPR was defined as the percentage of clinical pregnancies with two or more gestational sacs confirmed on ultrasound. Biochemical and ectopic pregnancies were considered non-viable pregnancies, with NVPR expressed as the percentage non-viable pregnancies per completed OS/IUI cycles. A secondary outcome of interest was ET (mm) on the day of hCG trigger, which was available for 2,017 of 4,773 cycles. Cycles with ET last checked before the day of hCG trigger (typically the day prior) were excluded from this analysis.
Statistical analysis Demographic factor comparisons between FPL groups were analyzed with Student t-tests, Mann Whitney U-tests, and χ2- tests, as appropriate. Multilevel random and fixed effects regression models were used to calculate odds ratios (ORs) for pregnancy outcomes and ET, with FPL analyzed first continuously, then by comparing FPL groups. An arbitrary cutoff at the
15th percentile of our population was selected to stratify cycles into a shorter FPL group (8 days) and a longer FPL group (>8 days).
All models adjusted for potential confounders including age, day 3 FSH, and BMI determined a priori as well as the effect of the same woman going through multiple cycles. Two sub-analyses were also performed. The first sub-analysis was limited to 2,017 of 4,773 cycles for which peak E2 was available on the day of hCG trigger such that cycles with peak E2 recorded before the day of hCG trigger (typically the day prior) were excluded. The second sub-analysis was limited to 3,911 cycles from women with ovulatory cycles, excluding cycles from women with diagnoses of polycystic ovarian syndrome or anovulation.
Finally, a ROC analysis was performed to determine whether a threshold FPL or ET existed for which clinical pregnancy varied significantly.
Results
Baseline patient demographics including age (years), BMI at cycle initiation (kg/m2), race, infertility diagnosis, day 3 FSH, gravidity, and parity are displayed in Table 1, stratified by FPL. As expected, women in the shorter FPL group were older with slightly higher (albeit within the normal range) day 3 FSH and higher incidence of idiopathic infertility and diminished ovarian reserve.
Table 2 summarizes the cycle characteristics for 4,773 completed gonadotropin OS/IUI cycles stratified by FPL. Among these cycles, FPL ranged from 6-38 days, with 729 cycles characterized by a shorter follicular phase (≤8 days) and 4044 characterized by a longer follicular phase (>8 days). While total gonadotropin dose was significantly different between the
two FPL groups (with a higher dose noted in the longer FPL group), response was similar between FPL groups, with similar peak E2. Number of follicles was also clinically similar between the two groups (median 2, interquartile range 1-2), albeit statistically different (p < 0.001). Notably, cycles with a longer follicular phase had increased ET as compared to cycles with a shorter follicular phase.
Results for pregnancy outcomes are summarized in Tables 3-4. All analyses adjusted for potential confounders including age, day 3 FSH, BMI, and the fact that some women underwent more than one cycle. When FPL was analyzed as a continuous variable, we found that the odds of clinical pregnancy increased by 6.0% with each additional day of the follicular phase (aOR 1.06, 95% CI 1.03-1.09, p < 0.001) (Table 3). When analyzing the FPL as a dichotomous variable, cycles with a longer compared to those with a shorter follicular phase resulted in significantly higher CPR (13.8 vs. 9.2%, p = 0.001). The adjusted odds for clinical pregnancy were 45% higher in the former compared to the latter group (aOR: 1.45, 95% CI: 1.07-1.97, p = 0.018). However, ROC analysis failed to identify a particular FPL cutoff that significantly impacted CPR (AUC = 0.57). FPL did not impact NVPR, SABR, or MPR in either analysis (Tables 3-4).
In order to account for a potential impact of follicular response on pregnancy outcomes, we performed a sub-analysis limited to the sub-group of 2,017 cycles for which serum peak E2 results were available on the day of hCG trigger. When pregnancy outcomes were analyzed including the effect of peak E2 in addition to the mixed effect of age, BMI, day 3 FSH, and woman in the adjusted models, the effect of FPL on pregnancy outcomes was in the same direction but attenuated, losing statistical significance for CPR in both the continuous analysis (aOR 1.03, 95% CI: 0.98-1.07, p = 0.262) and the dichotomous analysis (aOR 1.15, 95% CI: 0.69-1.88, p = 0.611) (Supplemental Table 3a and Table 4a).
Endometrial thickness was analyzed for this same subset of 2,017 cycles with ET available from day of hCG administration. Analysis of FPL as a continuous variable revealed that ET increased by 0.09 mm (95% CI: 0.06-0.12, p <0.001) with each additional day of the follicular phase. The adjusted mean difference between the longer and shorter follicular phase length groups was 1.08 mm (95% CI: 0.81-1.34, p < 0.001); however, an ROC analysis again failed to identify a specific FPL cutoff for which ET varied significantly (AUC = 0.5117).
A second sub-analysis limited to 3,911 cycles from women with ovulatory cycles was performed. When FPL was analyzed continuously, the association between FPL and clinical pregnancy was again attenuated (aOR 1.04, 95% CI 0.99-1.09) . However, in the dichotomous analysis, cycles characterized by a longer follicular phase had significantly higher CPR than cycles characterized by a shorter follicular phase (12.6% vs. 8.8%, p = 0.005) (Supplemental Table 3b and 4b). Additionally, median ET was significantly higher among cycles with a longer follicular phase (8.7mm, IQR 7.2mm-10mm) compared to those with a shorter follicular phase (7.3mm, IQR 6.3mm-8.7mm) (p <0.001).
Discussion
Gonadotropin OS/IUI is a commonly practiced first-line treatment for a wide range of infertility diagnoses. This study explored the effect of FPL on the outcome of gonadotropin OS/IUI cycles and found that a shorter follicular phase was associated with a decreased chance of clinical pregnancy, a finding that persisted even after adjustment for potential confounders including age and measures of ovarian reserve. The rates of non-viable pregnancy, spontaneous abortion, and multiple pregnancy were similar between FPL groups.
Consistent with prior studies of both natural and stimulated cycles (Lenton et al., 1984; Sherman and Korenman, 1975; Treloar et al., 1967), this study revealed variation in length of the follicular phase, with about 15 percent of women noted to have a shorter follicular phase of ≤8 days. Compared to women with a longer follicular phase, those with a shorter follicular phase tended to be older with a lower median BMI and a higher incidence of decreased ovarian reserve (as indicated by day 3 FSH levels) and idiopathic infertility, trends which have been previously welldocumented in the literature (Jukic et al., 2007; Kato et al., 1999; Lenton et al., 1984; Sherman and Korenman, 1975; Van Zonneveld et al., 2003) and for which our analyses were adjusted a priori. Despite these differences, the two FPL groups were comparable in the number of follicles produced per cycle (median two per cycle) and in peak E2 levels suggesting a similar response to stimulation after appropriate adjustments to the gonadotropin dose.
Our data suggest that among women undergoing gonadotropin OS/IUI cycles, even after controlling for the mixed effects of patients undergoing multiple cycles, age, BMI, and day 3 FSH, FPL may impact pregnancy outcomes. When FPL was analyzed as a continuous variable, CPR significantly increased with each day of the follicular phase, and when FPL was analyzed as a dichotomous variable (shorter vs. longer FPL), the results were similar, with a decreased chance of clinical pregnancy among women with a shorter FPL. However, ROC analysis failed to identify a critical FPL cutoff.
Our results support and strengthen the conclusions of previous studies on the effect of follicular phase length among women with infertility (Check et al., 2003, 1992; Khalil et al., 2001). Our study specifically adjusted for several important potential confounders, most notably markers of ovarian reserve, which were not accounted for in these earlier studies. Further, our study contained more than five times the number of cycles included in either of these previous studies. Our findings are, however, in contrast to more recent studies of women undergoing
ovarian stimulation for IVF cycles, which have not shown an effect of FPL on pregnancy outcomes (Alport et al., 2011; Mardešič et al., 2014; Martin et al., 2006). It is possible that women pursuing IUI represent a distinct patient population from those pursuing IVF, and that underlying differences between these two groups account for the differing impact of FPL. Alternatively, it could be that a difference in protocols accounts for the discrepant results. For example, the protocols used in two of the IVF studies involved administration of GnRH agonists starting from the mid-luteal phase of the previous cycle until the day of hCG trigger (Alport et al., 2011; Martin et al., 2006). Recent data suggests that use of GnRH agonists among infertile women with a shorter follicular phase may actually lengthen the follicular phase by about 3 days and partially restore fecundity (Cédrin-Durnerin et al., 2003), presumably by pituitary downregulation and inhibition of advanced follicular recruitment and development. The use of GnRH agonists may therefore mitigate the influence of FPL on cycle outcomes. Finally, and perhaps most importantly, the supraphysiologic levels of estrogens among women undergoing IVF may attenuate the negative effect on the endometrium induced by a shorter follicular phase. In contrast, peak E2 levels in OS/IUI cycles more closely resemble E2 levels in natural cycles, as demonstrated by the peak E2 levels in the present study. For these reasons, studies on follicular phase length pertaining specifically to patients undergoing ovarian stimulation for IVF are not applicable to patients undergoing stimulation for IUI, and the two should not be compared.
In regard to the effect of FPL on the endometrium, our data suggests that in cycles with a longer follicular phase, ET is increased. Numerous studies have correlated ET after ovarian stimulation with improved chance of conception during IVF (Gonen and Casper, 1990; Kovacs et al., 2003; Noyes et al., 1995; Richter et al., 2007), with most investigators agreeing that an ET of at least 6 mm is necessary for successful implantation (Gonen and Casper, 1990). Several recent studies suggest that ET is similarly correlated with increased chance of implantation and pregnancy during IUI cycles (Bromer et al., 2009; Esmailzadeh and Faramarzi, 2007; Maher et al., 2017;
Wolff et al., 2013). It is therefore possible that the effect of FPL on CPR may be partially attributable to increased time for endometrial development and potentially improved endometrial receptivity. While the difference in ET between those with a shorter versus longer FPL in our study was small and potentially clinically insignificant, the results highlight a biologically plausible mechanism that may partially explain the relationship between FPL and CPR.
Interestingly, in the sub-analysis limited only to those cycles with peak E2 levels available on day of hCG trigger, the noted differences persisted in the same direction but the effects were attenuated. This finding is suggestive of a possible impact of E2 on pregnancy outcomes, which is expected. However, given the FPL groups were similar in both median number of follicles and in median peak E2 levels, is seems unlikely that these variables would represent significant confounders. It is possible that the attenuated effect of FPL in the sub-analysis is a result of the smaller sample size, as more than half of patients last had E2 levels checked the day before rather than the day of hCG trigger and were therefore excluded from the subgroup. It is also worth noting that patients for whom E2 is measured on the day of hCG trigger in our practice tend to be those patients requiring closer monitoring during their cycle, including high responders and younger patients. It is therefore possible that the difference in magnitude of the FPL effect in the sub-analysis may in part be explained by underlying differences of the subgroup population rather than the effect of follicular response per se.
In the sub-analysis limited to women with ovulatory cycles, the relationship between FPL and CPR was also attenuated but persisted in the dichotomous analysis, with the longer FPL group demonstrating higher CPR and increased ET. The attenuation of the relationship between FPL and CPR in the continuous analysis after exclusion of patients with ovulatory disorders might be a reflection of this group’s more favorable prognosis with gonadotropin IUI (Mitwally and Casper, 2004). However, the persistence of the association in the dichotomous analysis (when
utilizing a cut-off identifying cycles with very short FPL) even after the exclusion of anovulatory cycles suggests that factors other than infertility diagnoses are responsible for the lower CPR observed in cycles with short FPL.
The data set reported in this study is one of the largest series to date of women undergoing gonadotropin OS/IUI. Patients with a wide range of demographic factors and infertility diagnoses were included, enhancing the generalizability of the data. The study is further strengthened by the uniformity of the protocol used, with all patients treated in one academic center with the same stimulation protocol using gonadotropins only. Finally, our study took into account and adjusted for the possible effect of both maternal age and diminished ovarian reserve on all outcomes.
The study has several notable limitations. First, clinical pregnancy was the primary outcome and not live birth because nearly 50% of the study population ultimately received their obstetrical care at outside facilities rendering delivery information difficult to obtain. While this is certainly a limitation of our study, clinical pregnancy remains a critically important outcome for reproductive endocrinologists that routinely discharge patients to OB care once viability is confirmed. Nevertheless, the relationship between FPL and clinical pregnancy remains of interest. Second, measures of ovarian reserve included day 3 FSH but not AMH levels. The main reason for this is the fact that this large database partially predates the now common practice of obtaining routine anti-Mullerian hormone (AMH) levels for ovarian reserve testing. As such, this variable was not included or adjusted for in our analyses. However, day 3 FSH remains a well-validated proxy for ovarian reserve and continues to be used to define and diagnose diminished ovarian reserve in clinical practice. Finally, the study is limited by its retrospective design. However, as it is not practical to randomize women to predetermined lengths of stimulation given the risks of
spontaneous ovulation or triggered ovulation of premature oocytes, retrospective studies of FPL among women undergoing gonadotropin OS/IUI have value.
In conclusion, our findings suggest that the duration of the follicular phase might be impacting certain outcomes of gonadotropin OS/IUI cycles, namely clinical pregnancy rates and endometrial thickness, although no critical FPL cutoff was identified. While a causal relationship cannot be established based on retrospective data, the reported association suggests that an ultra-short follicular phase may negatively impact the endometrial milieu, thereby impeding implantation and leading to lower clinical pregnancy rates. Further studies are necessary to determine whether manipulating FPL either by modifying hormonal stimulation protocols or adding GnRH agonists prior to cycle initiation could result in improved pregnancy rates in this population. Funding: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
References
Alport, B., Case, A., Lim, H., Baerwald, A., 2011. Does the Ovarian Stimulation Phase Length Predict In vitro Fertilization Outcomes ? Int. J. Fertil. Steril. 5, 134–141. Bromer, J.G., Aldad, T.S., Taylor, H.S., 2009. Defining the proliferative phase endometrial defect. Fertil. Steril. 91, 698–704. https://doi.org/10.1016/j.fertnstert.2007.12.066 Cédrin-Durnerin, I., Bstandig, B., Galey, J., Bry-Gauillard, H., Massin, N., Hugues, J.N., 2003. Beneficial effects of GnRH agonist administration prior to ovarian stimulation for patients with a short follicular phase. Reprod. Biomed. Online 7, 179–184. https://doi.org/10.1016/S1472-6483(10)61748-8
Check, J., Adelson, H., Lurie, D., Jamison, T., 1992. Effect of the Short Follicular Phase on Subsequent Conception. Gynecol. Obstet. Investiation 34, 180–183. Check, J., Liss, J., Shucoski, M., 2003. Effect of short follicular phase with follicular maturity on conception outcome. Clin. Exp. Obstet. Gynecol. 30, 195–196. Esmailzadeh, S., Faramarzi, M., 2007. Endometrial thickness and pregnancy outcome after intrauterine insemination. Fertil. Steril. 88, 432–437. https://doi.org/10.1016/j.fertnstert.2006.12.010 Gonen, Y., Casper, R.F., 1990. Prediction of implantation by the sonographic appearance of the endometrium during controlled ovarian stimulation for in vitro fertilization (IVF). J. In Vitro Fert. Embryo Transf. 7, 146–152. https://doi.org/10.1007/BF01135678 Jukic, A.M.Z., Weinberg, C.R., Baird, D.D., Wilcox, A.J., 2007. Lifestyle and Reproductive Factors Associated with Follicular Phase Length. J. Women’s Heal. 16, 1340–1347. https://doi.org/10.1089/jwh.2007.0354 Kato, I., Toniolo, P., Koenig, K.L., Shore, R.E., Zeleniuch-Jacquotte, A., Akhmedkhanov, A., Riboli, E., 1999. Epidemiologic correlates with menstrual cycle length in middle aged women. Eur. J. Epidemiol. 15, 809–14. Khalil, M.R., Rasmussen, P.E., Erb, K., Laursen, S.B., Rex, S., Westergaard, L.G., 2001. Homologous intrauterine insemination. An evaluation of prognostic factors based on a review of 2473 cycles. Acta Obstet. Gynecol. Scand. 80, 74–74. https://doi.org/10.1080/791201839 Klein, N.A., Harper, A.J., Houmard, B.S., Sluss, P.M., Soules, M.R., 2002. Is the short follicular phase in older women secondary to advanced or accelerated dominant follicle development? J. Clin. Endocrinol. Metab. 87, 5746–5750. https://doi.org/10.1210/jc.2002020622 Kovacs, P., Matyas, S., Boda, K., Kaali, S.G., 2003. The effect of endometrial thickness on IVF/ICSI outcome. Hum. Reprod. 18, 2337–2341. https://doi.org/10.1093/humrep/deg461
Lenton, E.A., Landgren, B.-M., Sexton, L., Harper, R., 1984. Normal variation in the length of the follicular phase of the menstrual cycle: effect of chronological age. Br. J. Obstet. An Int. J. Obstet. Gynaecol. 91, 681–684. https://doi.org/10.1111/j.1471-0528.1984.tb04830.x Maher, M.A., Abdelaziz, A., Shehata, Y.A., 2017. Effect of follicular diameter at the time of ovulation triggering on pregnancy outcomes during intrauterine insemination. Int. J. Gynecol. Obstet. 139, 174–179. https://doi.org/10.1002/ijgo.12291 Mardešič, T., Mannaerts, B., Abuzeid, M., Levy, M., Witjes, H., Fauser, B.C.J.M., 2014. Short follicular phase of stimulation following corifollitropin alfa or daily recombinant FSH treatment does not compromise clinical outcome: A retrospective analysis of the Engage trial. Reprod. Biomed. Online 28, 462–468. https://doi.org/10.1016/j.rbmo.2013.12.009 Martin, J.R., Mahutte, N.G., Arici, A., Sakkas, D., 2006. Impact of duration and dose of gonadotrophins on IVF outcomes. Reprod. Biomed. Online 13, 645–650. https://doi.org/10.1016/S1472-6483(10)60654-2 Mitwally, M.F.M., Casper, R.F., 2004. Aromatase inhibition reduces the dose of gonadotropin required for controlled ovarian hyperstimulation. J. Soc. Gynecol. Investig. 11, 406–415. https://doi.org/10.1016/j.jsgi.2004.03.006 Noyes, N., Liu, H.C., Sultan, K., Schattman, G., Rosenwaks, Z., 1995. Implantation: Endometrial thickness appears to be a significant factor in embryo implantation in in-vitro fertilization. Hum. Reprod. 10, 919–922. https://doi.org/10.1093/oxfordjournals.humrep.a136061 Richter, K.S., Bugge, K.R., Bromer, J.G., Levy, M.J., 2007. Relationship between endometrial thickness and embryo implantation, based on 1,294 cycles of in vitro fertilization with transfer of two blastocyst-stage embryos. Fertil. Steril. 87, 53–59. https://doi.org/10.1016/j.fertnstert.2006.05.064 Sherman, B.M., Korenman, S.G., 1975. Hormonal characteristics of the human menstrual cycle throughout reproductive life. J. Clin. Invest. 55, 699–706. https://doi.org/10.1172/JCI107979
Souter, I., Baltagi, L.M., Kuleta, D., Meeker, J.D., Petrozza, J.C., 2011. Women, weight, and fertility: The effect of body mass index on the outcome of superovulation/intrauterine insemination cycles. Fertil. Steril. 95, 1042–1047. https://doi.org/10.1016/j.fertnstert.2010.11.062 Treloar, A.E., Boynton, R.E., Behn, B.G., Brown, B.W., 1967. Variation of the human menstrual cycle through reproductive life. Int. J. Fertil. Steril. 12, 77–126. https://doi.org/10.1097/00006254-196801000-00019 Van Zonneveld, P., Scheffer, G.J., Broekmans, F.J.M., Blankenstein, M.A., De Jong, F.H., Looman, C.W.N., Habbema, J.D.F., Te Velde, E.R., 2003. Do cycle disturbances explain the age-related decline of female fertility? Cycle characteristics of women aged over 40 years compared with a reference population of young women. Hum. Reprod. 18, 495–501. https://doi.org/10.1093/humrep/deg138 Wolff, E.F., Bahidi, N., Alford, C., Richter, K., Widra, E., 2013. Influences on endometrial development during intrauterine insemination: clinical experience of 2,929 patients with unexplained infertility. Fertil. Steril. 100, 194–9. https://doi.org/10.1021/nl061786n.CoreShell
Jennifer Bakkensen received her B.S. from the University of North Carolina at Chapel Hill and M.D. from Weill Cornell Medical College. She is a resident in the Brigham and Women’s and Massachusetts General Hospital Residency in Obstetrics and Gynecology and plans to pursue a fellowship in Reproductive Endocrinology and Infertility.
Key message
This large-scale retrospective study suggests a possible relationship, independent of age and ovarian reserve, between follicular phase length, endometrial thickness, and clinical pregnancy rates specifically among women undergoing gonadotropin-induced OS/IUI, an important firstline infertility treatment. These findings may help physicians in counseling their patients on the likelihood of successful OS/IUI treatment.
Table 1. Baseline demographic characteristics of 2,054 patients
Age, years BMI, kg/m2 Race/ethnic group Caucasian Non-Caucasian Day 3 FSH levels, IU/l Infertility Diagnosis Unexplained Male Factor Anovulation Polycystic ovarian syndrome Diminished ovarian reserve Tubal Factor Uterine Factor Endometriosis Combined Factors Other Prior Gravidity Prior Parity
Shorter follicular phase ≤8 days N = 311 (15%) 37 (34-40) 22.6 (20.8-24.8)
Longer follicular phase >8 days N=1743 (85%) 35 (32-38) 23.4 (21.1-26.8)
171 (55) 140 (45) 7.5 (6.4-9.8)
850 (49) 893 (51) 7 (5.7-8.8)
112 (36) 28 (9) 5 (2) 4 (1)
595 (34) 211 (12) 122 (7) 159 (9)
82 (26)
232 (13)
10 (3) 4 (1) 6 (2) 47 (15) 11 (5) 143 (46) 72 (23)
56 (3) 12 (<1) 43 (2) 269 (15) 43 (4) 821 (47) 423 (24)
All values expressed as n (%) or median (interquartile range) as appropriate.
p-value
<.001 <.001 .760
<.001 <.001
.695 .664
Table 2. Cycle characteristics of 4,773 Gonadotropin OS/IUI cycles
Follicular phase length, days Total Gn dose, IU Peak E2a, pg/mL No of Follicles ≥13mmb Endometrial Thicknessa, mm
Shorter follicular phase ≤8 days N = 728 (15%) 8 (8-8)
Longer follicular phase >8 days N = 4045 (85%) 11 (10-13)
p-value
375 (300-750) 302 (223-452) 2 (1-2)
675 (462.5-1050) 306 (196-468) 2 (1-2)
<.001 .523 <.001
7.7 (6.7-9)
9 (7.7-10.2)
<.001
<.001
All values expressed as median (interquartile range). Among women who had E2 and endometrial thickness recorded on the day of the trigger (N = 2,017). b Recorded on the last visit prior to or on the day of trigger. a
Table 3. Effect of follicular phase length as a continuous variable (days) on clinical pregnancy outcomes
Clinical pregnancy Non-viable pregnancy Spontaneous abortion Multiple pregnancy
OR (95% CI) associated with each additional day of follicular phase 1.06 (1.03, 1.09) 1.03 (0.96, 1.11) 1.06 (1.00, 1.13) .99 (0.92, 1.06)
All models controlled for age, BMI, day 3 FSH, and woman
p-value
<.001 0.376 0.049 0.767
Table 4. Effect of follicular phase length as a dichotomous variable (shorter vs. longer follicular phase) on clinical pregnancy outcomes
Shorter follicular phase ≤8 days N = 728 (15%) Clinical pregnancy Non-viable pregnancy Spontaneous abortion Multiple pregnancy a
67 (9.2)
Longer p-value follicular phase >8 days N = 4045 (85%) 558(13.8) .001
11 (1.5)
61 (1.5)
.999
12 (17.9)
107 (19.2)
.792
5 (7.5)
73 (13.1)
.186
aOR (95% CI) a p-value
1.45 (1.07, 1.97) .88 (.45, 1.72)
.018
1.32 (.67, 2.61) 1.83 (.70, 4.75)
.425
.701
.215
Odds ratios for longer follicular phase versus the referent shorter follicular phase controlling for the mixed effect of woman, age, BMI, and day 3 FSH.