Optimal Timing of Delivery in Small for Gestational Age Fetuses Near Term

Abstract

Small for gestational age (SGA), or infants weighing below the 10th percentile at birth for their gestational age, is associated with unexplained stillbirth and other adverse neonatal outcomes. Considering these risks, it is not clear what gestational age timing of delivery is optimal for SGA fetuses. Many previous studies aiming to find the right delivery timing for SGA fetuses did not or were unable to consider the risk of neonatal death. The current study aimed to study the competing risks of perinatal mortality and morbidity comparing delivery versus postponement of delivery at varying gestational ages. The Netherlands Perinatal Registry was used to obtain data between 1999 and 2007 of singleton deliveries between 36 and 426/7 weeks’ gestation. Deliveries were assigned to 1 of 3 groups based on birth weight percentile for gestational age (SGA <5th percentile [SGA < P5] group, 61,021 deliveries; SGA 5th–10th percentile [SGA P5-P10] group, 58,902 deliveries; non-SGA group, 1,168,523 deliveries). The assignment of these groups was corrected for parity, fetal sex, and ethnic background. The 3 outcome measures used were neonatal mortality, antepartum stillbirth, and neonatal morbidity. Statistical significance was considered P < 0.01. In the SGA < P5 group, induced delivery was more common than in the P5-P10 and non-SGA groups (35.5%, 29.2%, and 29.9%; P < 0.0001). In the SGA < P5 group, stillbirth occurred in 8.0% of deliveries, whereas 2.6% of the SGA P5-P10 deliveries and 1.2% of non-SGA deliveries had stillbirth (both P < 0.0001). Intrapartum or neonatal mortality was also more common in the SGA groups, occurring in 5.9% of deliveries in the SGA < P5 group and 2.1% in the SGA P5-P10 group compared with 0.6% in the non-SGA group (both P < 0.0001). In the SGA groups, the combined perinatal mortality rates were minimized at 38 to 40 weeks’ gestation. At 38 and 39 weeks’ gestation, there was no difference in mortality between delivery at that week or delivery with expectant management for a week. At 40 weeks, perinatal mortality was reduced by delivery at that week as compared with expectant management for a week. Similarly, the neonatal morbidity outcomes declined from 36 to 39 weeks’ gestation, was stable from 39 to 40 weeks’ gestation, and increased at 41 weeks’ gestation. Considering mortality risk, the optimal delivery time for SGA < P5 deliveries and for non-SGA deliveries is 38 to 39 weeks, and the optimal delivery time for the SGA P5-P10 group is less clear. These results differ from the conclusion of a recent study that suggested SGA fetuses should be delivered at 37 to 38 weeks based on risk of stillbirth. This current study’s conclusion differs because, unlike the previous study, it takes into account the risk of intrapartum and neonatal mortality. These findings are also important as many clinicians induce at 36 or 37 weeks for suspected SGA fetuses.