Balancing the risks of stillbirth and neonatal death in the early preterm small-for-gestational-age fetus

Abstract

Timing of delivery for the early preterm small-for-gestational-age (SGA) fetus remains unknown. Our aim was to estimate the risk of stillbirth in the early preterm SGA fetus compared with the risk of neonatal death. We performed a retrospective cohort study of singleton pregnancies that underwent second-trimester anatomy ultrasound (excluding fetal anomalies, aneuploidy, and pregnancies with incomplete neonatal follow-up data). SGA was defined as birthweight <10th percentile by the Alexander standard. Life-table analysis was used to calculate the cumulative risks of stillbirth per 10,000 ongoing SGA pregnancies and of neonatal death per 10,000 SGA live births for 2-week gestational age strata in the early preterm period (24-33 weeks 6 days of gestation). We further examined the composite risk of expectant management and then compared the risk of expectant management with the risk of immediate delivery. Of 76,453 singleton pregnancies, 7036 SGA pregnancies that met inclusion criteria were ongoing at 24 weeks of gestation; there were 64 stillbirths, 226 live births, and 18 neonatal deaths from 24-33 weeks 6 days of gestation. As the risk of stillbirth increases with advancing gestational age, the risk of neonatal death falls, until the 32-33 weeks 6 days of gestation stratum. The relative risk of expectant management compared with immediate delivery remains <1 for each gestational age strata. Our findings suggest that the balance between the competing risks of stillbirth and neonatal death for the early preterm SGA fetus occurs at 32-33 weeks 6 days of gestation. These data can be useful when delivery timing remains uncertain.