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ORIGINAL RESEARCH |
From the Department of Obstetrics and Gynecology, Johns Hopkins University School of Medicine, Baltimore, Maryland; Ross University School of Medicine, Dominica, West Indies; and Department of Obstetrics, Greater Baltimore Medical Center, Baltimore, Maryland.
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ABSTRACT |
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METHODS: We reviewed the medical records of women who delivered a multiple gestation at 15 or more weeks at 2 institutions between January 1, 1990 and June 30, 2002 (n = 1,035). We recorded demographic data, medical complications, and pregnancy outcomes and analyzed these using paired t tests for continuous variables, 
2 for categorical variables, and linear regression analysis for the effect of multiple variables on the primary outcome variable, gestational age at delivery.
RESULTS: There was a statistically significant difference in mean gestational age at delivery (34 versus 34.9 weeks, P = .006) between the nulliparous and multiparous groups after excluding women with a history of previous preterm birth and/or midtrimester loss. There were no differences between groups in the likelihood of delivering before 20, 24, or 28 weeks. In linear regression analysis, ongoing fetal number (P < .001), premature rupture of membranes (PROM; P < .001), cerclage (P = .002), and death of 1 or more fetuses (P < .001) were associated with shorter gestation. Cesarean delivery was associated with longer gestation (P < .001). Nulliparous women were significantly more likely to have a pregnancy complicated by hypertension (20.8% versus 9.2%, P < .001), diabetes (7% versus 4%, P = .03), or PROM (24.4% versus 17.3%, P = .006).
CONCLUSION: Nulliparous women with a multiple gestation deliver their pregnancies, on average, 0.9 weeks earlier than parous women and more frequently experience hypertension, diabetes, and PROM. They are not, however, more likely to deliver before 24 weeks of gestation.
LEVEL OF EVIDENCE: II-3
Our primary goal was to investigate the influence of parity on gestational age at delivery of multiple gestations. Our hypothesis was that parity is protective with regards to gestational age at delivery as well as complications of pregnancy such as hypertension and premature rupture of membranes (PROM). That is, parous women with a multiple gestation may tolerate uterine overdistention better than nulliparas thereby allowing prolongation of gestation.
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MATERIALS AND METHODS |
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ABSTRACTMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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We reviewed delivery records to obtain obstetric history, the gestational age at and mode of delivery, and noted any medical complications for each woman. Obstetric complications analyzed included the presence of hypertension, diabetes, PROM, the placement of cerclage, intrauterine growth restriction, nonreassuring fetal heart rate, fetofetal transfusion syndrome, or intrauterine fetal death. We assigned each patient to either the nulliparous or the multiparous group. Nulliparity was defined as having no previous history of a delivery after 20 weeks of gestation. We compared these 2 groups with respect to maternal age, gestational age at delivery, and incidence of obstetric complications. We excluded women who delivered at less than 15 weeks of gestation to eliminate effects of fetal loss because of aneuploidy or voluntary termination, as well as one woman whose pregnancy spontaneously reduced from twins to a singleton gestation. A subanalysis of higher-order multiples or women with an ongoing fetal number of 3 or more was conducted with respect to gestational age at delivery and rate of pregnancy complications between nulliparous and multiparous groups. This was conducted once it was discovered that our nulliparous group had a significantly higher proportion of higher-order multiples. We analyzed the data using paired t tests for continuous variables, 2 for categorical variables and linear regression analysis for the effect of multiple variables on the primary outcome variable, gestational age at delivery.
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RESULTS |
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Figure 1 shows the incidence of cesarean delivery and obstetric complications in the 2 groups. Nulliparous women were significantly more likely to have a cesarean delivery. There was an increased likelihood of developing hypertension or diabetes, or experiencing preterm premature rupture of membranes in the nulliparous group. Otherwise, the incidence of other obstetric complications did not differ significantly between the 2 groups.
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In linear regression analysis, a higher ongoing fetal number, occurrence of PROM, cerclage placement, and death of at least one fetus were associated with a shorter gestational length. The incidence of cesarean delivery and diabetes increased as gestational age increased. Other factors analyzed that had no significant association with gestational age at delivery included the incidence of intrauterine growth restriction, hypertension, nonreassuring fetal heart tracing, fetofetal transfusion syndrome, and indicated delivery.
Table 2 summarizes the outcomes of higher-order multiple gestations. Although the mean maternal age remains similar in both groups, the difference between nulliparous and multiparous women with respect to the mean gestational age at delivery widens. With the exception of PROM, which continued to exhibit a higher frequency in nulliparous women, there were no differences between the groups in regards to perinatal complications.
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DISCUSSION |
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Until recently, studies have reported a positive correlation between perinatal complications and multiparity or grand multiparity.2,3,6 Our study indicates that parity offers a protective effect on gestational age at delivery in cases of multiple gestation. Nulliparous women with a twin gestation deliver their infants approximately 1 week earlier than their multiparous counterparts. Although this was a statistically significant difference in gestational age at delivery, 1 week may not be considered clinically significant. However, when higher-order multiples alone are considered, this gap widens to 3 weeks. Nulliparas are not, however, more likely to deliver before reaching a viable gestational age (24 weeks). After controlling for confounders, increasing fetal number, PROM, cerclage placement, and fetal death were associated with a shorter gestational length.
The increased use of assisted reproductive technologies in the nulliparous group may account for some of the complications noted in this group. Recent studies have suggested an increased risk of perinatal complications in women who have undergone in vitro fertilization as compared to women whose pregnancies were the result of spontaneous conception.7–9 Although the study by Moise et al7 included twins, the other 2 studies only included singleton gestations and thus their findings may not be applicable to our population of patients. There was an increased rate of preterm labor found in these studies in women who had undergone an assisted reproductive technique, although preterm PROM was not listed specifically as the cause for this finding.
Multiparous women with multiple gestations were not at higher risk for perinatal complications. In fact, nulliparous women were at significantly higher risk for premature rupture of membranes, hypertension, diabetes and cesarean delivery. When only higher-order multiples were considered, the incidence of PROM alone remained significantly different between the 2 groups. A drawback to the analysis of the higher-order multiples is the small sample size. Although the overall numbers are low, the trends seem to follow those observed in our total population. Thus, nulliparous women with a multiple gestation, especially those with higher-order multiples, should be monitored closely and counseled regarding their risk of PROM and earlier delivery. In addition, more concerted efforts to reduce the likelihood of multiple gestation, especially higher-order multiples, may be indicated in nulliparous women enrolled in assisted reproductive technology programs. Future studies may be directed at a possible cellular explanation for the adaptations of the uterine myometrium after previous uterine expansion.
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Footnotes |
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Address correspondence to: Abimbola J. Aina-Mumuney, MD, 600 North Wolfe St., Phipps 228; Baltimore, MD 21287; e-mail: aaina1{at}jhmi.edu.
10.1097/01.AOG.0000128905.37143.47
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REFERENCES |
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2. Babinszki A, Kerenyi T, Torok O, Grazi V, Lapinski R, Berkowitz RL. Perinatal outcome in grand and great-grand multiparity: effects of parity on obstetric risk factors. Am J Obstet Gynecol 1999;181:669–74.[Medline]
3. Petridou E, Salvanos H, Skalkidou A, Dessypris N, Moustaki M, Trichopoulos D. Are there common triggers of preterm deliveries? Br J Obstet Gynecol 2001;108:598–604.
4. Tarter JG, Khoury A, Barton JR, Jacques DL, Sibai BM. Demographic and obstetrical factors influencing pregnancy outcome in twin gestations. Am J Obstet Gynecol 2002;186:910–2.[Medline]
5. Russell RB, Petrini JR, Damus K, Mattison DR, Schwarz RH. The changing epidemiology of multiple births in the United States. Obstet Gynecol 2003;101:129–35.
6. Bai J, Wong FW, Bauman A, Mohsin M. Parity and pregnancy outcomes. Am J Obstet Gynecol 2002;186:274–8.[Medline]
7. Moise J, Laor A, Armon Y, Gur I, Gale R. The outcome of twin pregnancies after IVF. Hum Reprod 1998;13:1702–5.
8. Tan SL, Doyle P, Campbell S, Beral V, Rizk B, Brinsden P, et al. Obstetric outcome of in vitro fertilization pregnancies compared with normally conceived pregnancies. Am J Obstet Gynecol 1992;167:778–84.[Medline]
9. Wang JX, Norman RJ, Kristiansson P. The effects of various infertility treatments on the risk of preterm birth. Hum Reprod 2002;17:945–9.
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