Objective
We sought to estimate whether the presence of a maternal uterine anomaly is associated with adverse pregnancy outcomes.
Study Design
This retrospective cohort study included singleton pregnancies undergoing routine anatomic survey from 1990 through 2008 at a major tertiary care medical center. Pregnancies with a diagnosis of uterine anomaly (uterine septum, unicornuate uterus, bicornuate uterus, uterine didelphys) were compared to those with normal anatomy. Primary outcomes of interest were spontaneous preterm birth (PTB), breech presentation, and cesarean delivery.
Results
The presence of an anomaly was associated with PTB <34 weeks (adjusted odds ratio [aOR], 7.4; 95% confidence interval [CI], 4.8–11.4; P < .01), PTB <37 weeks (aOR, 5.9, 95% CI, 4.3–8.1; P < .01), primary nonbreech cesarean delivery (aOR, 2.6; 95% CI, 1.7–4.0; P < .01), preterm premature rupture of membranes (aOR, 3.2; 95% CI, 1.8–5.6; P < .01), and breech presentation (aOR, 8.6; 95% CI, 6.2–12.0; P < .01).
Conclusion
Women with a uterine anomaly are at risk for PTB, highlighting an at-risk population that needs additional study for possible interventions for PTB prevention.
The prevalence of müllerian anomalies is often derived from a primary infertility cohort, but the true prevalence among the general population is difficult to estimate. The most common müllerian anomalies include uterine septum, unicornuate uterus, bicornuate uterus, and uterine didelphys. Although it has been established that congenital uterine anomalies lead to infertility and recurrent first-trimester pregnancy loss, the relationship between uterine anomalies and adverse pregnancy outcomes in the third trimester is less well studied. Some who have found an association between uterine anomalies and preterm birth (PTB) theorize that diminished muscle mass, particularly in a unicornuate uterus, plays an important role in the mechanism of preterm delivery. The existing data linking the presence of uterine anomalies to outcomes such as PTB, preterm premature rupture of membranes (PPROM), breech presentation, and cesarean section are mostly derived from small case-control studies or case reports.
We aimed to improve upon the existing published data regarding congenital uterine anomalies and adverse pregnancy outcomes. We hypothesized that the presence of a uterine anomaly at routine ultrasound is associated with PTB, preterm rupture of membranes, and cesarean delivery.
Materials and Methods
We performed a retrospective cohort study to estimate the relationship between congenital uterine anomalies and adverse pregnancy outcomes. Our cohort was comprised of all consecutive singleton pregnancies undergoing routine anatomic survey from 1990 through 2008 at our tertiary care center. The study was conducted using the institutional perinatal database. Before study initiation, approval by our institutional human studies review board was obtained.
Women participating in the study had their demographic information, history, and pregnancy outcomes entered into a prenatal database. Since creation of the prenatal database in 1988, all of the patients seen in the prenatal diagnosis center have been followed by dedicated pregnancy outcome coordinators. To achieve complete follow-up information on pregnancy outcome, each patient was given a standardized form at the first visit to be completed after delivery, which detailed pregnancy outcome. The database included follow-up sheet also included details about pregnancy complications, delivery indications, and neonatal outcomes, including chromosomal and structural abnormalities. If the form was not returned within 4 weeks of expected date of delivery, the patient received a telephone call from an outcome coordinator. If the patient could not be reached after delivery, the referring physician was then contacted. For patients delivering within network, outcome information was extracted from the electronic medical record. Gestational age was determined by the first day of the woman’s last menstrual period (LMP). If the LMP-estimated due date was consistent (±5 days in the first trimester, ±14 days in the second trimester, and ±21 days in the third trimester) with the due date obtained from growth measurements at the first ultrasound then the due date was not changed. If the due dates by LMP and first ultrasound were not consistent, then the ultrasound-obtained due date was used to define gestational age. Maternal demographics, obstetric history, indications for the ultrasound visit, findings from the ultrasound examination or any testing performed, and outcome of the pregnancy were all collected and stored in the database. Patients with incomplete follow-up data were excluded from this study.
Evaluation of maternal uterine anatomy was performed as part of every routine anatomic survey. We defined the primary exposure as the presence of a uterine anomaly diagnosed prior to pregnancy or identified at that survey. We compared the incidence of adverse pregnancy outcomes in our 2 study populations: those with a congenital uterine anomaly vs those with normal uterine anatomy. Our primary outcomes were spontaneous PTB (both <34 weeks and <37 weeks), PPROM (defined as rupture of membranes <37 weeks), breech presentation, and cesarean delivery. Intrauterine growth restriction (IUGR) was defined as <10th percentile for gestational age.
The incidence of müllerian anomalies in our study population was estimated. Descriptive statistics were used to describe and compared the baseline characteristics of the 2 study groups. To compare baseline features between groups, Student t test was used for continuous variables, χ 2 for categorical variables, or Fisher exact test for rare categorical variables. Univariable analysis was used to estimate the relative risk (RR) of each outcome of interest (PTB, PPROM, breech, and cesarean delivery). We performed stratified analyses to identify potentially confounding factors. Logistic regression analyses were used to better estimate the relationship between uterine anomalies and our defined outcomes while adjusting for potentially confounding effects. Factors identified by the stratified analyses, as well as those with biological plausibility or historically reported to be associated with the outcomes of interest, were considered in the logistic regression analysis. Year of examination was considered categorically in increments of 4 years, to account for the long duration of the study period. Backward selection was used to reduce the number of variables in the model by assessing the magnitude of change in the effect size of the other covariates. Differences in the explanatory models were tested using the likelihood ratio test or Wald test. All variables that were statistically significant were included in the final models. A subgroup analysis of risk of PTB before both 34 and 37 weeks in women with a uterine anomaly compared to women with normal anatomy by parity (nulliparas vs multiparas) was performed. Descriptive analysis was used to estimate the incidence of various types of uterine anomalies within the primary exposure group and subgroup analysis to estimate the association between specific müllerian anomalies and risk of spontaneous PTB was also performed. All statistical analyses were performed using software (STATA 10.0, special edition; StataCorp, College Station, TX).
Results
Of 72,373 singleton pregnancies, 66,956 (93%) had complete pregnancy outcome information and were used in this analysis. A total of 203 (0.3%) pregnancies complicated by maternal uterine anomaly were identified at anatomic survey.
When comparing women with a uterine anomaly to those with normal uterine anatomy, the groups were statistically similar with respect to mean maternal age and gravidity. The incidence of preeclampsia and gestational diabetes was also statistically similar between the 2 groups. However, there were some differences. Women with a uterine anomaly were more likely to have a history of PTB or stillbirth. Women with normal uterine anatomy were more likely to have higher parity and to be African American ( Table 1 ).
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