- Email: [email protected]
The effect of low-dose aspirin on pregnancies complicated by elevated human chorionic gonadotropin levels
Wenstrom et al.
18. Heyl PS, Miller W, Canick JA. Maternal serum screening for aneuploid pregnancy by alpha-fetoprotein, hCG, and unconjugated estrioL Obstet Gynecol 1990;76:1025-31. 19. Fergnson-Smith MA, Yates JRW. Maternal age specific rates for chromosome aberrations and factors influencing them: report of a collaborative European study on 52,965 amniocenteses. Prenat Diagn 1984;4:5-44. 20. Steel MW, Breg WR. Chromosome analysis of human amniotic-fluid cells. Lancet 1966;1:383-5, 21. Simpson NE, Dallaire L, Miller JR, et al. Prenatal diagnosis of genetic disease in Canada: report of a collaborative study. Can Med AssocJ 1971;15:739. 22. American College of Obstetricians and Gynecologists. Antenatal diagnosis of genetic disorders. Washington: American College of Obstetricians and Gynecologists, 1976 May; ACOG Technical Bulletin no 39.
October 1995 Am J Obstet Gynecol
23. Burton BK, Prins GS, Verp MS. A prospective trial of prenatal screening for Down syndrome by means of maternal serum a-fetoprotein, human chorionic gonadotropin, and unconjugated estriol. AMJ OBSTETGYNECOL1993; 169:526-30. 24. Hook EB, Topoi BB, Cross PK. The natural history of cytogenetically abnormal fetuses detected at midtrimester amniocentesis which are not terminated electively: new data and estimates of the excess and relative risk of late fetal death associated with 47, +21 and some other abnormal karyotypes, ban J Hum Genet 1989;45:855-61. 25. Baird PA, Sadornik AD. Life expectancy in Down syndrome. J Pediatr 1987;110:849-54. 26. Jones KL. Smith's recognizable patterns of malformation. 4th ed. Philadelphia: WB Saunders, 1988:16-25.
The effect of low-dose aspirin on pregnancies complicated by elevated human chorionic gonadotropin levels Katharine D. Wenstrom, MD, John C. Hauth, MD, Robert L. Goldenberg, MD, Mary B. DuBard, MA, and Colleen Lea, BA Birmingham, Alabama OBJECTIVE: Our purpose was to determine whether elevated second-trimester human chorionic gonadotropin levels identify women likely to benefit from low-dose aspirin therapy. STUDY DESIGN: We evaluated second-trimester human chorionic gonadotropin levels obtained from healthy nulliparous women before screening for participation in a double-blind randomized trial of aspirin therapy: 262 women took 60 mg of aspirin daily and 420 did not. RESULTS: Among women who did not take aspirin, those with human chorionic gonadotropin levels >- 2.0 multiples of the median had a significantly lower mean birth weight (2859 vs 3159 gin, p = 0.04) than did those with normal human chorionic gonadotropin levels. All women who took aspirin had a higher mean birth weight than women who did not, but women with human chorionic gonadotropin levels >- 2.0 multiples of the median had the greatest increase (416.2 gm higher in those with human chorionic gonadotropin levels -> 2.0 multiples of the median, p = 0.02; 96 gm higher in those with human chorionic gonadotropin levels < 2.0 multiples of the median, p = 0.04). Regression analysis suggested that the higher birth weight was partly explained by a higher gestational age at delivery and partly by increased weight independent of gestational age. CONCLUSIONS: Aspirin therapy increased birth weight in all women, especially in women with high human chorionic gonadotropin levels, partly by increasing gestational age at delivery. This observation needs to be confirmed by further studies. (AM J OSSTETGYNECOL1995;173:1 292-6.)
Key words: Elevated h u m a n chorionic gonadotropin levels, low-dose aspirin From the Center for Obstetric Research, Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of Alabama at Birmingham. Supported in part by Agency for Health Care Policy Research contract No. 282-92-0055 and the National Institute of Child Health and Human Development grant No. RO1-HD24496-01. Presented in part at the Fifteenth Annual Meeting of the Society of Perinatal Obstetricians, Atlanta, Georgia, January 23-28, 1995. Reprint requests: Katharine D. Wenstrom, MD, University of Alabama at Birmingham, Department of Obstetrics and Gynecolog~ 618 S. 20th St., UAB Station, Birmingham, AL 35233-7333. Copyright © 1995 by Mosby-Year Book, Inc. 0002-9378/95 $5.00 + 0 6/6/66707 1292
T h e multiple-marker screening test for Down syndrome (maternal serum ot-fetoprotein [AFP], estriol, h u m a n chorionic gonadotropin [hCG], and maternal age) detects 58% to 91% of fetuses with Down syndrome in women o f all ages.~3 However, the positive predictive value of the multiple-marker screening test is only 4.3%. T h e majority o f abnormal results are therefore false positive. Evidence is now accumulating to show that pregnancies characterized by unexplained elevations of hCG (a typical feature of a false-positive mul-
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Wenstrom et al. 1293
Table I. Demographic characteristics of study groups Nonaspirin (n = 420)
Maternal age (yr)* Maternal race (%) Black White Gestational age at enrollment (wk)* Maternal weight at enrollment (kg)* Incidence of hCG levels - 2 . 0 MOM
Aspirin (n = 262)
Placebo (n = 249)
Failed run-in (n = 171)
Sig.ilicance
19.8 +_ 2.7
19.9 -- 2.8
19.8 -+ 3.1
NS
70 30 19.3 -+ 1.0 65.1 --- 15.2 7.6% (20/262)
73 27 19.4 -+ 1.1 65.5 _+ 15.5 7.9% (20/253)
81 19 19.4 + 1.! 64.2 -+ 16.9 4.3% (8/188)
p = 0.034 NS NS NS
NS, Not significant; MOM, multiples of the median.
* - 1 SD. tiple-marker screening test for Down syndrome) are at increased risk for complications, including preterm delivery, lower birth weight, and preeclampsia. 4-7 Analagous to unexplained elevated maternal serum AFP, unexplained elevated hCG is thought to reflect early placental damage or dysfunction that may predispose to later pregnancy problems. Daily low-dose aspirin therapy has been shown to reduce the occurrence of preeclampsia and increase birth weight in both low-risk women and in women with a p p a r e n t placental insufficiency.~ l0 Because preeclampsia and low birth weight are complications that may be heralded by elevated hCG levels, we hypothesized that patients with unexplained high secondtrimester hCG levels might benefit from low-dose aspirin therapy. We tested this hypothesis in 682 pregnant women who were screened for participation in a randomized, placebo-controlled trial of low-dose aspirin therapy conducted at the University of Alabama at Birmingham.
Material and methods T h e study population consisted of healthy, nulliparous women recruited to participate in an Institutional Review B o a r d - a p p r o v e d trial of the effects of low-dose aspirin therapy on the development of preeclampsia. T h e complete study protocol has been described elsewhere. 1° Inclusion criteria were age -< 28 years old; no history of renal disease, collagen vascular disease, diabetes mellitus, or chronic hypertension; and a singleton pregnancy. Eligible patients were contacted before 22 weeks' gestation. At the initial clinic screening visit, the medical and obstetric history was reviewed, gestational age was confirmed by ultrasonography, and blood was drawn for laboratory analysis. Maternal serum suitable for multiple-marker screening was obtained from approximately 83% of eligible participants (between 14 and 22 weeks' gestation) and stored at - 70 ° C. Patients who met all inclusion criteria were invited to participate in the study and were then further screened
in a 2-week run-in period. Patients who met all inclusion criteria and successfully completed the run-in period were then randomized to receive either one 60 mg capsule of aspirin or a placebo daily. Both patients and clinicians were blinded to the treatment received. Patients who failed the run-in period were not randomized and received routine care. All randomized patients were seen at 2-week intervals by the same antepartum team. Patients who were eligible for the study but failed the run-in received similar care in routine obstetric clinics supervised by University of Alabama personnel. Pregnancy outcome data were determined by the same reviewers for the randomized patients and for those patients who failed the run-in without knowledge of group assignment. Preeclampsia was defined as a diastolic blood pressure _>90 m m H g on two occasions at least 1 hour apart before or during labor or within 12 hours postpartum plus proteinuria -> 1 + on two or more occasions at least 1 hour apart (in the absence of a urinary tract infection or gross hematuria) or -> 0.5 gm p e r 24 hours. After completion of the aspirin trial, the stored maternal serum from all study patients was thawed and hCG levels were determined with a commercially available radioimmunoassay kit (Nichols Institute, San Juan, Capistrano, Calif.). Analyte levels were expressed as multiples of the median determined by comparison to the normal medians at 14 to 22 weeks' previously established for the patient population served by the University of Alabama. Stability of hCG through the freezing, storage, and thawing process was confirmed by testing control sera with known levels of hCG that had been frozen, stored, and thawed in a similar manner. Prestorage and poststorage hCG values were equivalent. Elevated hCG was defined as any value _>2.0 multiples of the median. 7 Patients were g r o u p e d according to whether they had elevated or normal hCG levels, and outcomes in women who were assigned to receive daily aspirin were c o m p a r e d with outcomes in those who were not. Statistical analysis was by X2 analysis with
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Am J Obstet Gynecol
Table II. Birth weight at delivery Birth weight (gm)* Patients
Aspirin (n = 262)
Nonaspirin (n = 420)
Difference with aspirin therapy
Significance
All patients hCG level < 2.0 MOM hCG level ->2.0 MOM
3257 - 574 3255 - 586 3275 -+ 412
3139 - 590 3159 -+ 570 2859 - 770
+118 +96 +416
p = 0.01 p = 0.04 p = 0.02
MOM, Multiples of the median. *4-1 SD. Fisher's exact test where appropriate. Further analysis was performed with linear regression techniques.
Results Two h u n d r e d sixty-two women successfully comp l e t e d the run-in and were assigned to take aspirin, whereas 420 were not assigned to aspirin (249 randomized to placebo and 171 failed the run-in and received routine care) (Table I). T h e maternal age, weight, gestational age at enrollment, and incidence of hCG levels >- 2.0 multiples of the median were similar among all three groups. Of the two groups who were not assigned to aspirin, the failed r u n - i n g r o u p included more black women (81% vs 73%) (p = 0.034). Because all other demographic characteristics and the incidence of the outcomes studied were the same in the placebo group and the failed run-in group (preeclampsia 5.6% vs 4.9%, m e a n birth weight 3162 gm vs 3104 gm, and mean gestational age at delivery 38.8 weeks vs 38.7 weeks), these two groups were combined for further analysis (nonaspirin group). T h e women in the combined nonaspirin group had a racial distribution similar to that of the aspirin group (76% black vs 70% black). Among all women who did not take aspirin, those with an hCG level > 2.0 multiples of the median had significantly lower mean birth weights than did those with an hCG level < 2.0 multiples of the median: 2859 gm versus 3159 gm, p = 0.04. Women with an hCG level > 2.0 multiples of the median were also delivered 1.2 weeks earlier than those with an hCG level < 2.0 multiples of the median (37.6 weeks vs 38.8 weeks), but this difference was not statistically significant (p = O.25). All women assigned to take aspirin had a significantly higher mean birth weight than all women who did not take aspirin: 3257 gm vs 3139 gm, p = 0.01 (Table II). W o m e n with an hCG level >- 2 multiples of the median who took aspirin had a mean 416 gm increase in birth weight c o m p a r e d with women with an hCG level > 2.0 multiples of the median who did not take aspirin and achieved a m e a n birth weight similar to women with an hCG level < 2.0 multiples of the median (p = 0.02). Women with an hCG level < 2 multiples of the median assigned to take aspirin had a 96 gm increase in birth
weight (p = 0.04) c o m p a r e d with women with an hCG level < 2.0 multiples of the median who did not take aspirin. The mean gestational age at delivery was also higher in women assigned to aspirin, although this difference did not reach statistical significance (1.5 weeks higher in those women with an hCG level _>2.0 multiples of the median, 0.3 weeks higher in those with an hCG level < 2.0 multiples of the median) (Table III). A regression model with birth weight as the dependent variable was used to determine the factors contributing to the mean 416 gm increase in birth weight among those women with an hCG level >- 2.0 multiples of the median who took aspirin. Seventy percent of the variance in birth weight was explained by the model. Belonging to the aspirin therapy group accounted for a 168 gm increase when maternal weight, race, gestational age at delivery, and the occurrence of preeclampsia were controlled for. The model indicated that much of the r e m a i n d e r of the increased birth weight associated with aspirin use was due to the 1.5-week increase in gestational age at delivery. Aspirin therapy was associated with a reduction in the incidence of preeclampsia in all women, regardless of hCG level: 1.9% (five of 262) with aspirin therapy versus 5.7% (24/420) without, p = 0.017 (Table IV). Women with an hCG level < 2.0 multiples of the median also experienced a reduction with aspirin therapy: 2.1% (five of 242) with aspirin therapy versus 5.4% (21/392) without, p = 0.04. Although the only patients with an hCG level >-2.0 multiples of the median who had preeclampsia did not take aspirin, the small numbers make speculations about the effect of aspirin therapy in this group impossible.
Comment Nationwide maternal serum AFP screening for fetal neural tube defects was initiated in the 1980s. It was recognized almost immediately that patients with unexplained or falsely elevated maternal serum AFP levels were at increased risk for suboptimal p r e g n a n c y outcomes. Both Brock et al. H and Wald et al. 1~ r e p o r t e d an association between elevated maternal serum AFP and low birth weight. Many subsequent publications have confirmed that unexplained elevated maternal serum
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Table I I I . Gestational age at delivery Gestational age at delivery (wk)* hCG
Aspirin (n = 262)
Nonaspirin (n = 420)
Difference with aspirin therapy
&gnificance
All patients hCG < 2.0 MOM hCG ->2.0 MOM
39.1 -+ 2.1 39.1 -+ 2.1 39.1 +- 1.8
38.8 -+ 2.6 38.8 -+ 2.5 37.6 + 3.9
+0.3 +0.3 + 1.5
p = 0.08 p = 0.15 p = 0.09
MOM, Multiples of the median. *+1 SD. Table IV. Incidence of preeclampsia Aspirin (n All patients hCG <2.0 MOM hCG _>2.0 MOM
262)
1.9% (5/262) 2.1% (5/242) 0% (0/20)
Nonaspirin (n = 420) 5.7% (24/420) 5.4% (21/392) 10.7% (3/28)
[
Significance p = 0.017 p = 0.04 p = 0.26
MOM, Multiples of the median. AFP is a marker for preterm birth, premature rupture of membranes, intrauterine growth restriction, and fetal deathJ~, 14 It is presumed that such elevations result from a breach in the placental-maternal interface and thus reflect placental vascular damage. Analogous to unexplained elevated maternal serum AFP levels, evidence is now accumulating to show that unexplained elevated hCG levels also predict poor pregnancy outcome, including preterm delivery, lower birth weight, and preeclampsia. 4' 5 However, rather than reflecting placental damage per se, it is likely that hCG levels rise in response to such damage. ~' ~6Both in vitro and clinical data support the speculation that early placental vascular damage leading to decreased oxygen supply results in increased hCG production by hyperplastic cytotrophoblast cells. When Fox and Path ~ maintained mature human placentas in organ culture at very low oxygen concentration (6% instead of the more physiologic 26%), there was a striking increase in the number of cytotrophoblastic cells. Crosignani ~6 reported a strong correlation between high third-trimester hCG levels and toxemia and conjectured that reduced oxygen supply to the cytotrophoblast caused a reactive hyperplasia and increased production of hCG. Since these early observations, numerous reports have suggested a link between elevated hCG levels and conditions associated with placental hypoxia, including hypertension, preterm delivery, low birth weight, and abruptio plcentae. 4-v Thus, although elevated maternal serum AFP levels suggest placental vascular damage, elevated hCG may reflect the placenta's attempt to compensate for such damage. In spite of these interesting observations the clinical importance of elevated maternal serum AFP and hCG levels as markers of a high-risk pregnancy has been questioned because, until now, there was no specific
therapy or management protocol that could be instituted to improve outcome after an abnormal test result. However, at least one specific intervention aimed at reducing placental vascular damage has been extensively tested, and that is low-dose aspirin therapy. Aspirin therapy appears to prevent vasoconstriction by reducing production of thromboxane A 2 and restoring a more normal thromboxane/prostacyclin ratio? ~ Aspirin is reported to reduce the incidence of pregnancy complications related to placental vascular compromise, including preeclampsia, pregnancy-induced hypertension, and intrauterine growth restriction. If elevated hCG levels reflect an attempt by the cytotrophoblast to compensate for placental vascular damage and low-dose aspirin prevents or reduces further vascular compromise, it seems logical to hypothesize that patients with unexplained high hCG levels might benefit from daily low-dose aspirin therapy. Our data indicate that women with an elevated hCG level have lower mean birth weights and are delivered earlier than those with a normal hCG level. Daily low-dose aspirin therapy improves outcome in women with unexplained elevated hCG levels by increasing birth weight. Interestingly, as indicated by our regression model, part of the increase in birth weight is explained by an increase in gestational age at delivery. Women with normal hCG levels also seemed to experience a reduction in the incidence of preeclampsia. If there is a real association between aspirin therapy and improved outcome, it may be that aspirin reduces placental vascular damage that could contribute to premature placental senescence. We could not evaluate the effect of aspirin therapy on the development of preeclampsia in women with an hCG level -> 2.0 multiples of the median because only three of the 48 women with elevated hCG had this
1296 Wenstrom et al.
complication. None of these women received aspirin. Power calculations (80% power, c~ = 0.05) indicate that 412 patients in each arm would be required to show that aspirin reduces the incidence of preeclampsia in women with elevated hCG levels (10.7%) to that of women with normal levels (5.4%) and 126 patients in each arm to show that aspirin reduces the incidence to that of women with normal hCG levels taking aspirin (2.1%). Nearly 1800 patients would need to be screened to identify 126 with hCG levels _ 2.0 multiples of the median and > 5880 to identify 412 patients with levels >-2.0 multiples of the median. In summary, daily low-dose aspirin therapy did increase birth weight and gestational age at delivery in patients with an unexplained elevated .hCG level. A larger trial is needed to confirm this finding and to fully evaluate aspirin's effects on the development of preeclampsia.
October 1995 Am J Obstet Gynecol
6.
7.
8.
9.
10. 11. 12.
REFERENCES
1. Haddow JE, Palomaki GE, Knight GJ, et al. Prenatal screening for Down's syndrome with Use of maternal serum markers. N Engl J Med 1992;327:588-93. 2. Cheng EY, Luthy DA, Zebelman AM, Williams MA, Lieppman RE, Hickok DE. A prospective evaluation of a secondtrimester screening test for fetal Down syndrome using maternal serum aipha-fetoprotein, hCG, and unconjugated estriol. Obstet Gynecol 1993;81:72-7. 3. Wenstrom KD, Williamson RA, Grant SS, Hudson JD, Getchell JP. Evaluation of multiple-marker screening for Down syndrome in a statewide population. AMJ OBSTET GYNECOL1993;169:793-7. 4. Gonen R, Perez R, David M, Dar H, Merksamer R, Sharf M. The association between unexplained second-trimester maternal serum hCG elevation and pregnancy complications. Obstet Gynecol 1992;80:83-6. 5. Tanaka M, Natori M, Kohno H, Ishimoto H, Kobayashi T,
13. 14.
15. 16.
17.
Nozawa S. Fetal growth in patients with elevated maternal serum hCG levels. Obstet Gynecol 1993;81:341-3. Lieppman RE, Williams MA, Cheng EY, et al. An association between elevated levels of human chorionic gonadotropin in the midtrimester and adverse pregnancy outcome. AMJ OBSTETGYNECOL1993;168:1852-7. Wenstrom KD, Owen J, Boots LR, DuBard MA. Elevated second-trimester human chorionic gonadotropin levels in association with poor pregnancy outcome. AM J OBSTET GYNECOL1994; 171 : 1038-41. Wallenburg HCS, Dekker GA, Mkovitz JW, Rotmans P. Low-dose aspirin prevents pregnancy-induced hypertension and pre-eclampsia in angiotensin-sensitive primigravidae. Lancet 1986;1:1-20. Schiff E, Peleg E, Goldenberg M, et al. The use of aspirin to prevent pregnancy-induced hypertension and lower the ratio of thromboxane A2 to prostacyclin in relatively high risk pregnancies. N Engl J Med 1989;321:351-6. Hauth JC, Goldenberg RL, Parker R, et al. Low-dose aspirin therapy to prevent preeclampsia. AM J OBSTET GYNECOL1993;168:1083-93. Brock DJH, Barron L, Jelen P, Watt M, Scrimgeour JB. Maternal serum alpha-fetoprotein measurements as an early indicator of low birth-weight. Lancet 1977;2:267-8. Wald N, Cuckle HS, Stirrat GM, Bennett MJ, Turnbull AC. Maternal serum alpha-fetoprotein and low birth-weight. Lancet 1977;2:268-70. Burton BK. Outcome of pregnancy in patients with unexplained elevated or low levels of maternal serum alphafetoprotein. Obstet Gynecol 1988;72:709-13. Waller DK, Lusfig LS, Cunningham GC, Golbus MS, Hook EB. Second-trimester maternal serum alpha-fetoprotein levels and the risk of subsequent fetal death. N EnglJ Med 1991;325:6-10. Fox H, Path MC. Effect of hypoxia on trophoblast in organ culture. AMJ OBSTETGYNECOL1970;7:1058-64. Crosignani PG. Correlation of human chorionic somatomammotropin (hCG) with fetal nutrition. In: Josimorich JB, ed. Lactogenic hormones, fetal nutrition and lactation. New York: John Wiley, 1973:203-20. Benigni A, Gregorini G, Frusca T. Effect of low-dose aspirin on fetal and maternal generation of thromboxane by platelets in women at risk for pregnancy-induced hypertension. N EnglJ Med 1989;321:357-62.
18. Heyl PS, Miller W, Canick JA. Maternal serum screening for aneuploid pregnancy by alpha-fetoprotein, hCG, and unconjugated estrioL Obstet Gynecol 1990;76:1025-31. 19. Fergnson-Smith MA, Yates JRW. Maternal age specific rates for chromosome aberrations and factors influencing them: report of a collaborative European study on 52,965 amniocenteses. Prenat Diagn 1984;4:5-44. 20. Steel MW, Breg WR. Chromosome analysis of human amniotic-fluid cells. Lancet 1966;1:383-5, 21. Simpson NE, Dallaire L, Miller JR, et al. Prenatal diagnosis of genetic disease in Canada: report of a collaborative study. Can Med AssocJ 1971;15:739. 22. American College of Obstetricians and Gynecologists. Antenatal diagnosis of genetic disorders. Washington: American College of Obstetricians and Gynecologists, 1976 May; ACOG Technical Bulletin no 39.
October 1995 Am J Obstet Gynecol
23. Burton BK, Prins GS, Verp MS. A prospective trial of prenatal screening for Down syndrome by means of maternal serum a-fetoprotein, human chorionic gonadotropin, and unconjugated estriol. AMJ OBSTETGYNECOL1993; 169:526-30. 24. Hook EB, Topoi BB, Cross PK. The natural history of cytogenetically abnormal fetuses detected at midtrimester amniocentesis which are not terminated electively: new data and estimates of the excess and relative risk of late fetal death associated with 47, +21 and some other abnormal karyotypes, ban J Hum Genet 1989;45:855-61. 25. Baird PA, Sadornik AD. Life expectancy in Down syndrome. J Pediatr 1987;110:849-54. 26. Jones KL. Smith's recognizable patterns of malformation. 4th ed. Philadelphia: WB Saunders, 1988:16-25.
The effect of low-dose aspirin on pregnancies complicated by elevated human chorionic gonadotropin levels Katharine D. Wenstrom, MD, John C. Hauth, MD, Robert L. Goldenberg, MD, Mary B. DuBard, MA, and Colleen Lea, BA Birmingham, Alabama OBJECTIVE: Our purpose was to determine whether elevated second-trimester human chorionic gonadotropin levels identify women likely to benefit from low-dose aspirin therapy. STUDY DESIGN: We evaluated second-trimester human chorionic gonadotropin levels obtained from healthy nulliparous women before screening for participation in a double-blind randomized trial of aspirin therapy: 262 women took 60 mg of aspirin daily and 420 did not. RESULTS: Among women who did not take aspirin, those with human chorionic gonadotropin levels >- 2.0 multiples of the median had a significantly lower mean birth weight (2859 vs 3159 gin, p = 0.04) than did those with normal human chorionic gonadotropin levels. All women who took aspirin had a higher mean birth weight than women who did not, but women with human chorionic gonadotropin levels >- 2.0 multiples of the median had the greatest increase (416.2 gm higher in those with human chorionic gonadotropin levels -> 2.0 multiples of the median, p = 0.02; 96 gm higher in those with human chorionic gonadotropin levels < 2.0 multiples of the median, p = 0.04). Regression analysis suggested that the higher birth weight was partly explained by a higher gestational age at delivery and partly by increased weight independent of gestational age. CONCLUSIONS: Aspirin therapy increased birth weight in all women, especially in women with high human chorionic gonadotropin levels, partly by increasing gestational age at delivery. This observation needs to be confirmed by further studies. (AM J OSSTETGYNECOL1995;173:1 292-6.)
Key words: Elevated h u m a n chorionic gonadotropin levels, low-dose aspirin From the Center for Obstetric Research, Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, University of Alabama at Birmingham. Supported in part by Agency for Health Care Policy Research contract No. 282-92-0055 and the National Institute of Child Health and Human Development grant No. RO1-HD24496-01. Presented in part at the Fifteenth Annual Meeting of the Society of Perinatal Obstetricians, Atlanta, Georgia, January 23-28, 1995. Reprint requests: Katharine D. Wenstrom, MD, University of Alabama at Birmingham, Department of Obstetrics and Gynecolog~ 618 S. 20th St., UAB Station, Birmingham, AL 35233-7333. Copyright © 1995 by Mosby-Year Book, Inc. 0002-9378/95 $5.00 + 0 6/6/66707 1292
T h e multiple-marker screening test for Down syndrome (maternal serum ot-fetoprotein [AFP], estriol, h u m a n chorionic gonadotropin [hCG], and maternal age) detects 58% to 91% of fetuses with Down syndrome in women o f all ages.~3 However, the positive predictive value of the multiple-marker screening test is only 4.3%. T h e majority o f abnormal results are therefore false positive. Evidence is now accumulating to show that pregnancies characterized by unexplained elevations of hCG (a typical feature of a false-positive mul-
Volume 173, Number 4 Am J Obstet Gynecol
Wenstrom et al. 1293
Table I. Demographic characteristics of study groups Nonaspirin (n = 420)
Maternal age (yr)* Maternal race (%) Black White Gestational age at enrollment (wk)* Maternal weight at enrollment (kg)* Incidence of hCG levels - 2 . 0 MOM
Aspirin (n = 262)
Placebo (n = 249)
Failed run-in (n = 171)
Sig.ilicance
19.8 +_ 2.7
19.9 -- 2.8
19.8 -+ 3.1
NS
70 30 19.3 -+ 1.0 65.1 --- 15.2 7.6% (20/262)
73 27 19.4 -+ 1.1 65.5 _+ 15.5 7.9% (20/253)
81 19 19.4 + 1.! 64.2 -+ 16.9 4.3% (8/188)
p = 0.034 NS NS NS
NS, Not significant; MOM, multiples of the median.
* - 1 SD. tiple-marker screening test for Down syndrome) are at increased risk for complications, including preterm delivery, lower birth weight, and preeclampsia. 4-7 Analagous to unexplained elevated maternal serum AFP, unexplained elevated hCG is thought to reflect early placental damage or dysfunction that may predispose to later pregnancy problems. Daily low-dose aspirin therapy has been shown to reduce the occurrence of preeclampsia and increase birth weight in both low-risk women and in women with a p p a r e n t placental insufficiency.~ l0 Because preeclampsia and low birth weight are complications that may be heralded by elevated hCG levels, we hypothesized that patients with unexplained high secondtrimester hCG levels might benefit from low-dose aspirin therapy. We tested this hypothesis in 682 pregnant women who were screened for participation in a randomized, placebo-controlled trial of low-dose aspirin therapy conducted at the University of Alabama at Birmingham.
Material and methods T h e study population consisted of healthy, nulliparous women recruited to participate in an Institutional Review B o a r d - a p p r o v e d trial of the effects of low-dose aspirin therapy on the development of preeclampsia. T h e complete study protocol has been described elsewhere. 1° Inclusion criteria were age -< 28 years old; no history of renal disease, collagen vascular disease, diabetes mellitus, or chronic hypertension; and a singleton pregnancy. Eligible patients were contacted before 22 weeks' gestation. At the initial clinic screening visit, the medical and obstetric history was reviewed, gestational age was confirmed by ultrasonography, and blood was drawn for laboratory analysis. Maternal serum suitable for multiple-marker screening was obtained from approximately 83% of eligible participants (between 14 and 22 weeks' gestation) and stored at - 70 ° C. Patients who met all inclusion criteria were invited to participate in the study and were then further screened
in a 2-week run-in period. Patients who met all inclusion criteria and successfully completed the run-in period were then randomized to receive either one 60 mg capsule of aspirin or a placebo daily. Both patients and clinicians were blinded to the treatment received. Patients who failed the run-in period were not randomized and received routine care. All randomized patients were seen at 2-week intervals by the same antepartum team. Patients who were eligible for the study but failed the run-in received similar care in routine obstetric clinics supervised by University of Alabama personnel. Pregnancy outcome data were determined by the same reviewers for the randomized patients and for those patients who failed the run-in without knowledge of group assignment. Preeclampsia was defined as a diastolic blood pressure _>90 m m H g on two occasions at least 1 hour apart before or during labor or within 12 hours postpartum plus proteinuria -> 1 + on two or more occasions at least 1 hour apart (in the absence of a urinary tract infection or gross hematuria) or -> 0.5 gm p e r 24 hours. After completion of the aspirin trial, the stored maternal serum from all study patients was thawed and hCG levels were determined with a commercially available radioimmunoassay kit (Nichols Institute, San Juan, Capistrano, Calif.). Analyte levels were expressed as multiples of the median determined by comparison to the normal medians at 14 to 22 weeks' previously established for the patient population served by the University of Alabama. Stability of hCG through the freezing, storage, and thawing process was confirmed by testing control sera with known levels of hCG that had been frozen, stored, and thawed in a similar manner. Prestorage and poststorage hCG values were equivalent. Elevated hCG was defined as any value _>2.0 multiples of the median. 7 Patients were g r o u p e d according to whether they had elevated or normal hCG levels, and outcomes in women who were assigned to receive daily aspirin were c o m p a r e d with outcomes in those who were not. Statistical analysis was by X2 analysis with
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Table II. Birth weight at delivery Birth weight (gm)* Patients
Aspirin (n = 262)
Nonaspirin (n = 420)
Difference with aspirin therapy
Significance
All patients hCG level < 2.0 MOM hCG level ->2.0 MOM
3257 - 574 3255 - 586 3275 -+ 412
3139 - 590 3159 -+ 570 2859 - 770
+118 +96 +416
p = 0.01 p = 0.04 p = 0.02
MOM, Multiples of the median. *4-1 SD. Fisher's exact test where appropriate. Further analysis was performed with linear regression techniques.
Results Two h u n d r e d sixty-two women successfully comp l e t e d the run-in and were assigned to take aspirin, whereas 420 were not assigned to aspirin (249 randomized to placebo and 171 failed the run-in and received routine care) (Table I). T h e maternal age, weight, gestational age at enrollment, and incidence of hCG levels >- 2.0 multiples of the median were similar among all three groups. Of the two groups who were not assigned to aspirin, the failed r u n - i n g r o u p included more black women (81% vs 73%) (p = 0.034). Because all other demographic characteristics and the incidence of the outcomes studied were the same in the placebo group and the failed run-in group (preeclampsia 5.6% vs 4.9%, m e a n birth weight 3162 gm vs 3104 gm, and mean gestational age at delivery 38.8 weeks vs 38.7 weeks), these two groups were combined for further analysis (nonaspirin group). T h e women in the combined nonaspirin group had a racial distribution similar to that of the aspirin group (76% black vs 70% black). Among all women who did not take aspirin, those with an hCG level > 2.0 multiples of the median had significantly lower mean birth weights than did those with an hCG level < 2.0 multiples of the median: 2859 gm versus 3159 gm, p = 0.04. Women with an hCG level > 2.0 multiples of the median were also delivered 1.2 weeks earlier than those with an hCG level < 2.0 multiples of the median (37.6 weeks vs 38.8 weeks), but this difference was not statistically significant (p = O.25). All women assigned to take aspirin had a significantly higher mean birth weight than all women who did not take aspirin: 3257 gm vs 3139 gm, p = 0.01 (Table II). W o m e n with an hCG level >- 2 multiples of the median who took aspirin had a mean 416 gm increase in birth weight c o m p a r e d with women with an hCG level > 2.0 multiples of the median who did not take aspirin and achieved a m e a n birth weight similar to women with an hCG level < 2.0 multiples of the median (p = 0.02). Women with an hCG level < 2 multiples of the median assigned to take aspirin had a 96 gm increase in birth
weight (p = 0.04) c o m p a r e d with women with an hCG level < 2.0 multiples of the median who did not take aspirin. The mean gestational age at delivery was also higher in women assigned to aspirin, although this difference did not reach statistical significance (1.5 weeks higher in those women with an hCG level _>2.0 multiples of the median, 0.3 weeks higher in those with an hCG level < 2.0 multiples of the median) (Table III). A regression model with birth weight as the dependent variable was used to determine the factors contributing to the mean 416 gm increase in birth weight among those women with an hCG level >- 2.0 multiples of the median who took aspirin. Seventy percent of the variance in birth weight was explained by the model. Belonging to the aspirin therapy group accounted for a 168 gm increase when maternal weight, race, gestational age at delivery, and the occurrence of preeclampsia were controlled for. The model indicated that much of the r e m a i n d e r of the increased birth weight associated with aspirin use was due to the 1.5-week increase in gestational age at delivery. Aspirin therapy was associated with a reduction in the incidence of preeclampsia in all women, regardless of hCG level: 1.9% (five of 262) with aspirin therapy versus 5.7% (24/420) without, p = 0.017 (Table IV). Women with an hCG level < 2.0 multiples of the median also experienced a reduction with aspirin therapy: 2.1% (five of 242) with aspirin therapy versus 5.4% (21/392) without, p = 0.04. Although the only patients with an hCG level >-2.0 multiples of the median who had preeclampsia did not take aspirin, the small numbers make speculations about the effect of aspirin therapy in this group impossible.
Comment Nationwide maternal serum AFP screening for fetal neural tube defects was initiated in the 1980s. It was recognized almost immediately that patients with unexplained or falsely elevated maternal serum AFP levels were at increased risk for suboptimal p r e g n a n c y outcomes. Both Brock et al. H and Wald et al. 1~ r e p o r t e d an association between elevated maternal serum AFP and low birth weight. Many subsequent publications have confirmed that unexplained elevated maternal serum
Volume 173, Number 4 Am J Obstet Gynecol
Wenstrom et al.
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Table I I I . Gestational age at delivery Gestational age at delivery (wk)* hCG
Aspirin (n = 262)
Nonaspirin (n = 420)
Difference with aspirin therapy
&gnificance
All patients hCG < 2.0 MOM hCG ->2.0 MOM
39.1 -+ 2.1 39.1 -+ 2.1 39.1 +- 1.8
38.8 -+ 2.6 38.8 -+ 2.5 37.6 + 3.9
+0.3 +0.3 + 1.5
p = 0.08 p = 0.15 p = 0.09
MOM, Multiples of the median. *+1 SD. Table IV. Incidence of preeclampsia Aspirin (n All patients hCG <2.0 MOM hCG _>2.0 MOM
262)
1.9% (5/262) 2.1% (5/242) 0% (0/20)
Nonaspirin (n = 420) 5.7% (24/420) 5.4% (21/392) 10.7% (3/28)
[
Significance p = 0.017 p = 0.04 p = 0.26
MOM, Multiples of the median. AFP is a marker for preterm birth, premature rupture of membranes, intrauterine growth restriction, and fetal deathJ~, 14 It is presumed that such elevations result from a breach in the placental-maternal interface and thus reflect placental vascular damage. Analogous to unexplained elevated maternal serum AFP levels, evidence is now accumulating to show that unexplained elevated hCG levels also predict poor pregnancy outcome, including preterm delivery, lower birth weight, and preeclampsia. 4' 5 However, rather than reflecting placental damage per se, it is likely that hCG levels rise in response to such damage. ~' ~6Both in vitro and clinical data support the speculation that early placental vascular damage leading to decreased oxygen supply results in increased hCG production by hyperplastic cytotrophoblast cells. When Fox and Path ~ maintained mature human placentas in organ culture at very low oxygen concentration (6% instead of the more physiologic 26%), there was a striking increase in the number of cytotrophoblastic cells. Crosignani ~6 reported a strong correlation between high third-trimester hCG levels and toxemia and conjectured that reduced oxygen supply to the cytotrophoblast caused a reactive hyperplasia and increased production of hCG. Since these early observations, numerous reports have suggested a link between elevated hCG levels and conditions associated with placental hypoxia, including hypertension, preterm delivery, low birth weight, and abruptio plcentae. 4-v Thus, although elevated maternal serum AFP levels suggest placental vascular damage, elevated hCG may reflect the placenta's attempt to compensate for such damage. In spite of these interesting observations the clinical importance of elevated maternal serum AFP and hCG levels as markers of a high-risk pregnancy has been questioned because, until now, there was no specific
therapy or management protocol that could be instituted to improve outcome after an abnormal test result. However, at least one specific intervention aimed at reducing placental vascular damage has been extensively tested, and that is low-dose aspirin therapy. Aspirin therapy appears to prevent vasoconstriction by reducing production of thromboxane A 2 and restoring a more normal thromboxane/prostacyclin ratio? ~ Aspirin is reported to reduce the incidence of pregnancy complications related to placental vascular compromise, including preeclampsia, pregnancy-induced hypertension, and intrauterine growth restriction. If elevated hCG levels reflect an attempt by the cytotrophoblast to compensate for placental vascular damage and low-dose aspirin prevents or reduces further vascular compromise, it seems logical to hypothesize that patients with unexplained high hCG levels might benefit from daily low-dose aspirin therapy. Our data indicate that women with an elevated hCG level have lower mean birth weights and are delivered earlier than those with a normal hCG level. Daily low-dose aspirin therapy improves outcome in women with unexplained elevated hCG levels by increasing birth weight. Interestingly, as indicated by our regression model, part of the increase in birth weight is explained by an increase in gestational age at delivery. Women with normal hCG levels also seemed to experience a reduction in the incidence of preeclampsia. If there is a real association between aspirin therapy and improved outcome, it may be that aspirin reduces placental vascular damage that could contribute to premature placental senescence. We could not evaluate the effect of aspirin therapy on the development of preeclampsia in women with an hCG level -> 2.0 multiples of the median because only three of the 48 women with elevated hCG had this
1296 Wenstrom et al.
complication. None of these women received aspirin. Power calculations (80% power, c~ = 0.05) indicate that 412 patients in each arm would be required to show that aspirin reduces the incidence of preeclampsia in women with elevated hCG levels (10.7%) to that of women with normal levels (5.4%) and 126 patients in each arm to show that aspirin reduces the incidence to that of women with normal hCG levels taking aspirin (2.1%). Nearly 1800 patients would need to be screened to identify 126 with hCG levels _ 2.0 multiples of the median and > 5880 to identify 412 patients with levels >-2.0 multiples of the median. In summary, daily low-dose aspirin therapy did increase birth weight and gestational age at delivery in patients with an unexplained elevated .hCG level. A larger trial is needed to confirm this finding and to fully evaluate aspirin's effects on the development of preeclampsia.
October 1995 Am J Obstet Gynecol
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