The risk of stillbirth and infant death by each additional week of expectant management in twin pregnancies

Objective The objective of the study was to compare the fetal/infant mortality risk associated with each additional week of expectant management with the mortality risk of immediate delivery in women with twin gestations. Study Design A retrospective cohort study was performed utilizing 2006-2008 National linked birth certificate and death certificate data. The incidence of stillbirth and infant death were determined for each week of pregnancy from 32 0/7 weeks' through 40 6/7 weeks' gestation. Pregnancies complicated by fetal anomalies were excluded. These measures were combined to estimate the theoretic risk of remaining pregnant an additional week by adding the risk of stillbirth during the extra week of pregnancy with the risk of infant death encountered with delivery during the following week. This composite fetal/infant mortality risk was compared with the risk of infant death associated with delivery at the corresponding gestational age. Results The risk of stillbirth increased with increasing gestational age, for example, between 37 and 38 weeks' gestation (12.5 per 10,000 vs 22.5 per 10,000; P <.05). As expected, the risk of infant death following delivery gradually decreased as pregnancies approached term gestation. Week-by-week differences were statistically significant (P <.05) between 32 and 36 weeks with decreasing risk of infant death at advancing gestational ages. The composite risk of stillbirth and infant death associated with an additional week of pregnancy had a significant increase from 37 to 38 weeks' gestation (43.9 per 10,000 vs 59.2 per 10,000; P <.05). At 37 weeks' gestation, the relative risk of mortality was statistically significantly lower with immediate delivery as compared with expectant management (relative risk, 0.87; 95% confidence interval, 0.77-0.99). Conclusion Our results suggest that fetal/infant death risk is minimized at 37 weeks' gestation; however, individual maternal and fetal characteristics must also be taken into account when determining the optimal timing of delivery for twin pregnancies.