Objective: To estimate the frequency of fetal death in multifetal pregnancies and the probability of survival to age 1 year for twins or triplets in which at least one fetal death occurred at 20 weeks' gestation or more.
Methods: We used the Matched Multiple Birth File from the US National Center for Health Statistics, which included 152,233 sets of twins and 5356 sets of triplets registered from 1995 to 1997. The Cox proportional hazards model was used to estimate the adjusted relative risk of death before age 1 year for remaining twins and triplets.
Results: Fetal death at 20 weeks' gestation or later was uncommon, occurring in 2.6% of twin and 4.3% of triplet gestations. After adjustment for confounders, the survival of the remaining fetuses was inversely related to the time of the first fetal demise. Same-sex twins were two times more likely than opposite-sex twins to die after an intrauterine demise at 25-32 weeks' gestation and were more than three times more likely to die after a death at 33 weeks' gestation or more.
Conclusion: After a fetal death in a multifetal pregnancy at 20 weeks' gestation or later, the survival of the remaining fetuses is inversely related to the time the death occurred. Among twins, survival also depends on sex concordance, with opposite-sex twins more likely than same-sex twins to survive.