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The relationship between follicle diameter, fertilization rate, and microscopic embryo quality
FERTILITY AND STERILITY
Vol. 55, No.1, January 1991
Printed on acid·free paper in U.S.A.
Copyright" 1991 The American Fertility Society
The relationship between follicle diameter, fertilization rate, and microscopic embryo quality
Christopher J. Haines, F.R.A.C.O.G.* Allison L. Emes Reproductive Medicine Programme, The Flinders University and Flinders Medical Centre, Adelaide, South Australia
The precision with which ovarian follicles can be identified and aspirated for in vitro fertilization (IVF) has improved with the development of highresolution transvaginal ultrasound (US) equipment. It is now possible to clearly identify follicles of 10 mm diameter or less, but few studies have investigated whether the oocytes retrieved from these potentially immature follicles are capable of achieving satisfactory fertilization rates in vitro. 1 •2 Aspiration ofthese small follicles adds to the duration of the procedure, carries a potentially higher risk of operative morbidity by increasing the total number of punctures necessary, and requires a greater input of laboratory resources than if they were ignored. The purpose of this prospective study was to assess the laboratory outcome of oocytes recovered from follicles of various diameters and to determine whether the aspiration of smaller follicles was justified. MATERIALS AND METHODS
The oocytes for assessment in this study were recovered from 26 patients having consecutive oocyte retrievals for IVF. Ovarian hyperstimulation was achieved using clomiphene citrate (Clomid; Merrell Dow, Sydney, Australia) 50 mg on days 5 to 9 of the cycle with human menopausal gonadotropin (Humegon; Organon, Oss, Holland) 150 IU from day 6 onward and continued according to ovarian response. The cycle was monitored using daily esReceived March 20, 1990; revised and accepted August 16, 1990. *Reprint requests and present address: Christopher J. Haines, F.R.A.C.O.G., Department of Obstetrics and Gynaecology, Prince of Wales Hospital, Shatin, N.T., Hong Kong. Vol. 55, No.1, January 1991
tradiol (E 2 ) assays (ER/155A; Baxter Clinical Assays, Dudingen, Switzerland) and US examinations that were performed from day 9 of the cycle. Human chorionic gonadotropin (hCG, Profasi; Serono, Aubonne, Switzerland), 10,000 IU, was administered when the leading follicle was at least 18 mm in diameter in the absence of a precipitous fall in E 2 or the suggestion of premature luteinization. The oocyte retrieval was performed approximately 35 hours after hCG by transvaginal US-guided aspiration using intravenous analgesia. 3 An Ausonics 357 MI 1,000 sector scanner (Ausonics Pty Ltd., Sydney, Australia) with a 7.5 mHz vaginal probe was used in all cases. For the purposes ofthe study, follicles were measured immediately before aspiration, and a record was maintained for each oocyte retrieved from a measured follicle. The diameter recorded was the average of two measurements made perpendicular to each other, all measurements being made by one operator. Follicle diameters were divided into three groups: group A consisting of follicles > 20 mm diameter; group B follicles 15 to 19 mm; and group C, follicles 10 to 14 mm. A double lumen needle was used for this study to limit confusion about the origin of each oocyte. The system was flushed at the end of each aspirate. If there was any doubt about the origin of a particular oocyte, these results were excluded. Also excluded were aspirates containing two or more oocytes and all cases in which a semen factor existed or in which there was a previous record of poor fertilization. The oocytes were inseminated 4 to 6 hours after retrieval and were examined 12 to 16 hours after insemination. The resulting embryos were graded using a modification ofthe scoring system of Cummins et al. 4 This is :1 microscopic asHaines and Emes
Communications-in-brief
205
Table 1 Relationship Between Follicular Diameter and Oocyte Fertilization Rate Follicular diameter"
No. of oocytes
No. fertilized
Fertilized b
28 46 26
27 39 20
96 84 76
%
mm
Group A GroupB GroupC
20+ 15 to 19 10 to 14
DISCUSSION
Values are means. b x 2 = 4.365, P = 0.1128. a
sessment of embryo quality using four grades, with grade 4 representing the embryos of highest quality. The relationship between fertilization rate and follicle diameter was examined using x2 analysis and Kendall's tau was used when comparing embryo quality with follicular diameter. RESULTS
A total of 100 oocytes were recovered from 26 treatment cycles (mean = 4.2, range 2 to 8). The highest fertilization rate was found in the group A follicles, with 27 of 28 (96.4%) oocytes achieving fertilization. In group B, 39 of 46 (84.8%) were fertilized, and in group C, 20 of 26 (76.9%). The differences in fertilization rate between individual groups were not significant (P = 0.1128). These results are summarized in Table 1. The comparison between embryo quality expressed as a grade and follicular diameter is presented in Table 2. With grade 4 representing the embryos of highest quality, 14 of 27 (52%) in group A, 19 of 39 (49%) in group B, and 6 of 20 (30%) in group C were in this category. Similar results were found with grade 3 embryos, in which 11 of 27 (41%), 16 of 39 (41%), and 7 of 20 (35%) were found, respectively, in each ofthe groups. For grade 2 embryos, however, there were 2 from 27 (7%) in group A, 4 from 39 (10%) in group B, and 5 from 20 (25%) in group C. No grade 1 embryos developed from oocytes retrieved from larger folliTable 2
cles (groups A and B), but 2 (10%) were derived from oocytes in group C. Although embryo quality improved with increasing follicle diameter, the difference was not highly significant (P = 0.026).
The relationship between follicle size, oocyte recovery, and fertilization rate have been studied using various methods to measure follicles including calculations based on volume of fluid aspirated1 and direct observation at laparoscopy or US. 5 More recently, follicles were measured by transvaginal US at the time of oocyte retrieval in a manner similar to that described in this study. 6 Using nuclear maturation for grading oocytes, follicles of 15 to 17 mm, 18 to 20 mm and >21 mm in diameter were found to produce similar numbers of mature oocytes (55%, 59%, and 56%, respectively}. In the group offollicles 12 to 14 mm, 30% of oocytes were mature (P < 0.01) and for follicles< 11 mm, only 9% (P < 0.001) produced mature oocytes. In our study, the selection of groups into which follicles of different size were divided was made on a clinical assumption that follicles :s; 14 mm were more likely to contain immature oocytes and those >20 mm had a higher chance of being postmature. Rather than using an index of nuclear maturation to assess the effect of follicular diameter, we measured the percentage fertilization rate for oocytes recovered from measured follicles and the quality of embryos that subsequently developed. Although we had been expecting the 15 to 19 mm group to provide the best outcome, this was not the case, and there was a trend toward an improved fertilization rate and embryo quality with increasing follicular size, the best results occurring in group A, which contained follicles > 20 mm. When comparisons were made between groups, however, no difference in fertilization rate existed. Embryo quality was found to improve as the follicles became larger, but this improvement was not
Relationship Between Follicular Diameter and Embryo Quality Follicular diameter"
Grade4
Grade3
Grade2
14 (52)c 19 (49) 6 (30)
11 (41) 16 (41) 7 (35)
4 (10) 5 (25)
Grade 1
Not fertilized
2 (10)
1 7 6
mm
Group A GroupB Group C a b
20+b 15 to 19b 10to14b
Values are means. Kendall's tau= 0.17, P = 0.026.
206
Haines and Emes
Communications-in-brief
2 (7)
c
Values in parentheses are percents.
Fertility and Sterility
highly significant. We therefore conclude that it is worthwhile continuing to aspirate smaller follicles in an attempt to achieve the maximum benefit from each cycle of IVF treatment.
SUMMARY
The diameter of preovulatory ovarian follicles was measured at the time of transvaginal USguided oocyte retrieval, and the oocytes were subsequently examined to assess fertilization rates and the quality of developing embryos. With follicles divided into three groups of increasing diameter, there were no significant differences in the fertilization rates of oocytes recovered from follicles of different size. Embryo quality improved with increasing follicle size, although the differences were not highly significant. Our results demonstrate that an acceptable laboratory outcome can be achieved with oocytes retrieved from smaller sized follicles.
Vol. 55, No.1, January 1991
REFERENCES 1. Lopata A, Brown JB, Leeton JF, Talbot JM, Wood C: In vitro fertilization of preovulatory oocytes and embryo transfer in infertile patients treated with clomiphene and human chorionic gonadotropin. Fertil Steril 30:27, 1978 2. Wood C, Leeton J, Talbot JM, Trounson AO: Technique for collecting mature human oocytes for in vitro fertilization. Br J Obstet Gynaecol88:756, 1981 3. Haines CJ, O'Shea RT, Weiss TJ, Emes AL: Transvaginal ultrasound-guided oocyte retrieval using intravenous analgesia. Clin Reprod Fertil 5:263, 1987 4. Cummins JM, Breen TM, Harrison KL, Shaw JM, Wilson LM, Hennessey JK: A formula for scoring human embryo growth rates in in vitro fertilization: its value in predicting pregnancy and in comparison with visual estimates of embryo quality. J In Vitro Fert Embryo Transfer 3:284, 1986 5. Quigley MM, Wolf DP, Makled NF, Dandekar PV, Sokoloski JE: Follicular size and number in human in vitro fertilization. Fertil Steril 38:678, 1982 6. Scott RT, Hofman GE, Muasher SJ, Acosta AA, Kreiner DK, Rosenwaks Z: Correlation of follicular diameter with oocyte recovery and maturity at the time of transvaginal follicular aspiration. J In Vitro Fert Embryo Transfer 6:73, 1989
Haines and Emes Communications-in-brief
207
Vol. 55, No.1, January 1991
Printed on acid·free paper in U.S.A.
Copyright" 1991 The American Fertility Society
The relationship between follicle diameter, fertilization rate, and microscopic embryo quality
Christopher J. Haines, F.R.A.C.O.G.* Allison L. Emes Reproductive Medicine Programme, The Flinders University and Flinders Medical Centre, Adelaide, South Australia
The precision with which ovarian follicles can be identified and aspirated for in vitro fertilization (IVF) has improved with the development of highresolution transvaginal ultrasound (US) equipment. It is now possible to clearly identify follicles of 10 mm diameter or less, but few studies have investigated whether the oocytes retrieved from these potentially immature follicles are capable of achieving satisfactory fertilization rates in vitro. 1 •2 Aspiration ofthese small follicles adds to the duration of the procedure, carries a potentially higher risk of operative morbidity by increasing the total number of punctures necessary, and requires a greater input of laboratory resources than if they were ignored. The purpose of this prospective study was to assess the laboratory outcome of oocytes recovered from follicles of various diameters and to determine whether the aspiration of smaller follicles was justified. MATERIALS AND METHODS
The oocytes for assessment in this study were recovered from 26 patients having consecutive oocyte retrievals for IVF. Ovarian hyperstimulation was achieved using clomiphene citrate (Clomid; Merrell Dow, Sydney, Australia) 50 mg on days 5 to 9 of the cycle with human menopausal gonadotropin (Humegon; Organon, Oss, Holland) 150 IU from day 6 onward and continued according to ovarian response. The cycle was monitored using daily esReceived March 20, 1990; revised and accepted August 16, 1990. *Reprint requests and present address: Christopher J. Haines, F.R.A.C.O.G., Department of Obstetrics and Gynaecology, Prince of Wales Hospital, Shatin, N.T., Hong Kong. Vol. 55, No.1, January 1991
tradiol (E 2 ) assays (ER/155A; Baxter Clinical Assays, Dudingen, Switzerland) and US examinations that were performed from day 9 of the cycle. Human chorionic gonadotropin (hCG, Profasi; Serono, Aubonne, Switzerland), 10,000 IU, was administered when the leading follicle was at least 18 mm in diameter in the absence of a precipitous fall in E 2 or the suggestion of premature luteinization. The oocyte retrieval was performed approximately 35 hours after hCG by transvaginal US-guided aspiration using intravenous analgesia. 3 An Ausonics 357 MI 1,000 sector scanner (Ausonics Pty Ltd., Sydney, Australia) with a 7.5 mHz vaginal probe was used in all cases. For the purposes ofthe study, follicles were measured immediately before aspiration, and a record was maintained for each oocyte retrieved from a measured follicle. The diameter recorded was the average of two measurements made perpendicular to each other, all measurements being made by one operator. Follicle diameters were divided into three groups: group A consisting of follicles > 20 mm diameter; group B follicles 15 to 19 mm; and group C, follicles 10 to 14 mm. A double lumen needle was used for this study to limit confusion about the origin of each oocyte. The system was flushed at the end of each aspirate. If there was any doubt about the origin of a particular oocyte, these results were excluded. Also excluded were aspirates containing two or more oocytes and all cases in which a semen factor existed or in which there was a previous record of poor fertilization. The oocytes were inseminated 4 to 6 hours after retrieval and were examined 12 to 16 hours after insemination. The resulting embryos were graded using a modification ofthe scoring system of Cummins et al. 4 This is :1 microscopic asHaines and Emes
Communications-in-brief
205
Table 1 Relationship Between Follicular Diameter and Oocyte Fertilization Rate Follicular diameter"
No. of oocytes
No. fertilized
Fertilized b
28 46 26
27 39 20
96 84 76
%
mm
Group A GroupB GroupC
20+ 15 to 19 10 to 14
DISCUSSION
Values are means. b x 2 = 4.365, P = 0.1128. a
sessment of embryo quality using four grades, with grade 4 representing the embryos of highest quality. The relationship between fertilization rate and follicle diameter was examined using x2 analysis and Kendall's tau was used when comparing embryo quality with follicular diameter. RESULTS
A total of 100 oocytes were recovered from 26 treatment cycles (mean = 4.2, range 2 to 8). The highest fertilization rate was found in the group A follicles, with 27 of 28 (96.4%) oocytes achieving fertilization. In group B, 39 of 46 (84.8%) were fertilized, and in group C, 20 of 26 (76.9%). The differences in fertilization rate between individual groups were not significant (P = 0.1128). These results are summarized in Table 1. The comparison between embryo quality expressed as a grade and follicular diameter is presented in Table 2. With grade 4 representing the embryos of highest quality, 14 of 27 (52%) in group A, 19 of 39 (49%) in group B, and 6 of 20 (30%) in group C were in this category. Similar results were found with grade 3 embryos, in which 11 of 27 (41%), 16 of 39 (41%), and 7 of 20 (35%) were found, respectively, in each ofthe groups. For grade 2 embryos, however, there were 2 from 27 (7%) in group A, 4 from 39 (10%) in group B, and 5 from 20 (25%) in group C. No grade 1 embryos developed from oocytes retrieved from larger folliTable 2
cles (groups A and B), but 2 (10%) were derived from oocytes in group C. Although embryo quality improved with increasing follicle diameter, the difference was not highly significant (P = 0.026).
The relationship between follicle size, oocyte recovery, and fertilization rate have been studied using various methods to measure follicles including calculations based on volume of fluid aspirated1 and direct observation at laparoscopy or US. 5 More recently, follicles were measured by transvaginal US at the time of oocyte retrieval in a manner similar to that described in this study. 6 Using nuclear maturation for grading oocytes, follicles of 15 to 17 mm, 18 to 20 mm and >21 mm in diameter were found to produce similar numbers of mature oocytes (55%, 59%, and 56%, respectively}. In the group offollicles 12 to 14 mm, 30% of oocytes were mature (P < 0.01) and for follicles< 11 mm, only 9% (P < 0.001) produced mature oocytes. In our study, the selection of groups into which follicles of different size were divided was made on a clinical assumption that follicles :s; 14 mm were more likely to contain immature oocytes and those >20 mm had a higher chance of being postmature. Rather than using an index of nuclear maturation to assess the effect of follicular diameter, we measured the percentage fertilization rate for oocytes recovered from measured follicles and the quality of embryos that subsequently developed. Although we had been expecting the 15 to 19 mm group to provide the best outcome, this was not the case, and there was a trend toward an improved fertilization rate and embryo quality with increasing follicular size, the best results occurring in group A, which contained follicles > 20 mm. When comparisons were made between groups, however, no difference in fertilization rate existed. Embryo quality was found to improve as the follicles became larger, but this improvement was not
Relationship Between Follicular Diameter and Embryo Quality Follicular diameter"
Grade4
Grade3
Grade2
14 (52)c 19 (49) 6 (30)
11 (41) 16 (41) 7 (35)
4 (10) 5 (25)
Grade 1
Not fertilized
2 (10)
1 7 6
mm
Group A GroupB Group C a b
20+b 15 to 19b 10to14b
Values are means. Kendall's tau= 0.17, P = 0.026.
206
Haines and Emes
Communications-in-brief
2 (7)
c
Values in parentheses are percents.
Fertility and Sterility
highly significant. We therefore conclude that it is worthwhile continuing to aspirate smaller follicles in an attempt to achieve the maximum benefit from each cycle of IVF treatment.
SUMMARY
The diameter of preovulatory ovarian follicles was measured at the time of transvaginal USguided oocyte retrieval, and the oocytes were subsequently examined to assess fertilization rates and the quality of developing embryos. With follicles divided into three groups of increasing diameter, there were no significant differences in the fertilization rates of oocytes recovered from follicles of different size. Embryo quality improved with increasing follicle size, although the differences were not highly significant. Our results demonstrate that an acceptable laboratory outcome can be achieved with oocytes retrieved from smaller sized follicles.
Vol. 55, No.1, January 1991
REFERENCES 1. Lopata A, Brown JB, Leeton JF, Talbot JM, Wood C: In vitro fertilization of preovulatory oocytes and embryo transfer in infertile patients treated with clomiphene and human chorionic gonadotropin. Fertil Steril 30:27, 1978 2. Wood C, Leeton J, Talbot JM, Trounson AO: Technique for collecting mature human oocytes for in vitro fertilization. Br J Obstet Gynaecol88:756, 1981 3. Haines CJ, O'Shea RT, Weiss TJ, Emes AL: Transvaginal ultrasound-guided oocyte retrieval using intravenous analgesia. Clin Reprod Fertil 5:263, 1987 4. Cummins JM, Breen TM, Harrison KL, Shaw JM, Wilson LM, Hennessey JK: A formula for scoring human embryo growth rates in in vitro fertilization: its value in predicting pregnancy and in comparison with visual estimates of embryo quality. J In Vitro Fert Embryo Transfer 3:284, 1986 5. Quigley MM, Wolf DP, Makled NF, Dandekar PV, Sokoloski JE: Follicular size and number in human in vitro fertilization. Fertil Steril 38:678, 1982 6. Scott RT, Hofman GE, Muasher SJ, Acosta AA, Kreiner DK, Rosenwaks Z: Correlation of follicular diameter with oocyte recovery and maturity at the time of transvaginal follicular aspiration. J In Vitro Fert Embryo Transfer 6:73, 1989
Haines and Emes Communications-in-brief
207