Correlation between prenatal and neonatal birth order in twin pregnancy

Little data is available correlating the in utero order of presentation and the birth order of twins. Our objective was to determine whether birth order in twin pregnancies corresponds to the order of presentation early in pregnancy. All twin pregnancies in which amniocentesis was performed from 1996 to 1998 were identified. Those with discordant genders that delivered at our hospital were included. Order of presentation was documented by ultrasound at the time of amniocentesis. Delivery data were obtained from review of medical records. Statistical comparison was done using two-tailed Fisher's exact test, Student's t-test, and Mann-Whitney U test. Sixty patients met inclusion criteria. Birth order corresponded to the order at the time of amniocentesis in 55 of 60 cases (91.7%). There was no difference in the rate of concordance of prenatal and neonatal birth order in twins delivered vaginally compared with those delivered abdominally (90.9 vs. 91.8%, p = 1.0). Cases with discordant prenatal and neonatal birth order had similar maternal ages, gestational ages at amniocentesis and delivery, and fetal presentation at delivery as cases with concordant birth orders. In dichorionic twin pregnancies, birth order is established early in gestation in >90% of cases regardless of route of delivery.