The impact of chorionicity on maternal pregnancy outcomes

OBJECTIVE: Women carrying twin pregnancies often receive similar counseling, regardless of chorionicity, with the notable exception of twin-twin transfusion syndrome (TTTS); however, little is known about whether the presence of 1 vs 2 placentas confers dissimilar maternal risks. We sought to determine differences in maternal and neonatal outcomes based on chorionicity. STUDY DESIGN: This was a retrospective cohort study of all twin pregnancies at our institution undergoing routine second-trimester ultrasound for anatomic survey from 1990 through 2010. Secondary outcomes included other adverse maternal and neonatal outcomes. Relative risks and adjusted odds ratios (aORs) were calculated. Cluster analysis was used to account for nonindependence of twin pairs. RESULTS: Of 2301 pregnancies, 1747 (75.9%) were dichorionic and 554 (24.1%) were monochorionic. Rates of preeclampsia, gestational diabetes, placental abruption, placenta previa, preterm labor, and preterm premature rupture of membranes (PPROM) were not significantly different in dichorionic vs monochorionic pregnancies. Early preterm delivery less than 34 weeks (aOR, 1.47; 95% confidence interval [CI], 1.17-1.86) and less than 28 weeks (aOR, 2.58; 95% CI, 1.58-4.20) were more likely in monochorionic twins, as was neonatal intensive care unit admission (aOR, 1.41; 95% CI, 1.12-1.78). Monochorionic twins delivered earlier at a mean gestational age of 34.2 weeks vs 35.0 weeks for dichorionic twins (P < .001). Hospital length of stay was significantly longer for monochorionic twins with a mean of 13.7 days vs 10.8 days for dichorionic twins (P = .01). CONCLUSION: There are no significant differences in maternal outcomes by chorionicity; however, monochorionicity is associated with increased fetal risks. This information may be helpful in guiding more targeted counseling to expectant parents of twins that, although the presence of an additional placenta does not confer additional maternal risks, monochorionic infants tend to deliver earlier and require longer hospital stays.