Optimal timing of delivery in small for gestational age fetuses near term: a national cohort study

Our aim was to study the competing risks of antepartum versus intrapartum/neonatal death in small for gestational age (SGA) and non-SGA fetuses.

We performed a national cohort study using all singletons delivered between 36 and 42(6/7) weeks without hypertension, preeclampsia, diabetes, congenital anomalies, or noncephalic presentation from the Netherlands Perinatal Registry (1999-2007). The resultant cohort was divided in three groups based on birth weight by gestational age (SGA < P5 group, 61,021 deliveries; SGA P5-10 group, 58,902 deliveries; non-SGA group 1,168,523 deliveries). We compared the mortality risk of delivery with expectant management.

Delivery was associated with more mortality than expectant management for 1 week from 39 weeks onward in the non-SGA group (relative risk [RR], 1.26; 95% confidence interval [CI], 1.05-1.50). For the SGA < P5, expectant management for 1 more week was associated with more mortality from 38 weeks onward although this only reached statistical significance from 40 weeks onward (RR, 2.46; 95% CI, 1.80-3.36).

At 36 and 37 weeks, delivery is associated with a higher risk of mortality in SGA < P5 fetuses than expectant management. Delivery of SGA < P5 fetuses at 38 and 39 weeks is associated with the best perinatal outcome whereas for non-SGA fetuses this is at 39 to 40 weeks.