REESTIMATING DATE OF DELIVERY IN MULTIFETAL PREGNANCIES

Objective.-To clarify the optimal estimated date of delivery for multi fetal pregnancies. Design, Subjects, and Setting.-A retrospective stud y of all 88 936 infants born of multifetal pregnancies and all 6 020 5 42 infants born of singleton pregnancies that occurred at 26 weeks or more of gestation between 1989 and 1993 in Japan. Main Outcome Measure .-Incidence of stillbirth and early neonatal death according to gestat ional age at delivery. Results.-The mean+/-SD duration of pregnancy wa s 37.0+/-2.7 weeks for multifetal pregnancies and 39.6+/-1.6 weeks for singleton pregnancies. In multifetal pregnancies, the incidence of st illbirth and of early neonatal death gradually declined until 37 to 38 weeks' gestation and then increased. These parameters in singleton pr egnancies declined until 39 weeks' gestation before increasing. The lo west incidence of perinatal death (stillbirth plus early neonatal deat h) seen at 38 weeks' gestation in multifetal pregnancies corresponded to that seen at 43 weeks' gestation in singleton pregnancies (10.5 vs 9.7 per 1000 infants). The risk of perinatal death was more than 6 tim es as high for fetuses of multifetal pregnancies born at 37 weeks or l ater than for singleton fetuses born at 40 weeks or later (relative ri sk, 6.6; 95% confidence interval, 6.1-7.1). Conclusion.-Fetuses of mul tifetal pregnancies are at an increased risk of death after reaching t he normative gestational age for singleton pregnancies. Limiting the e stimated date of delivery to 37 to 38 weeks may be appropriate in mult ifetal pregnancies.