The probability of multiple births when multiple gestational sacs or viable embryos are diagnosed at first trimester ultrasound.

The live birth outcome when multiple gestational sacs were diagnosed at first trimester ultrasound was reviewed in 227 twin, 43 triplet and five quadruplet pregnancies. When two gestational sacs were present, the probability of delivering twins was 63% for maternal age less than 30 and 52% for maternal age greater than or equal to 30. With three gestational sacs, the probability of a triplet birth was 45% for maternal age less than 30 and 18% for maternal age greater than or equal to 30. When two viable embryos were present, the probability of a twin birth was 90% for maternal age less than 30 and 84% for maternal age greater than or equal to 30. With three viable embryos, the probability of a triplet birth was 90% for maternal age less than 30 and 44% for maternal age greater than or equal to 30. Two gestations resulting from ovulation induction with clomiphene citrate were more likely to result in twin delivery at term, compared to spontaneous twin gestations (P = 0.012). These findings may be useful in the treatment and management of patients when multiple gestations are diagnosed early in pregnancy.