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

OBJECTIVE: 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. STUDY DESIGN: 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 birth-weight < 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. RESULTS: 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. CONCLUSION: 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.