In their excellent article, Mandujano et al performed a brilliant analysis comparing fetal and neonatal mortality by week of gestation, including the risk of remaining undelivered, to determine the best gestational age of delivery.
In the low-risk cohort, the total number of deaths after 34 +0 weeks of gestation is 16,639. The estimated minimum total number of losses that would occur (after 34 +0 weeks) if all the remaining fetuses in the beginning of each week were delivered during this specific week is 13,669 and corresponds to 38 weeks’ gestation (38 +0 to 38 +6 ) in the low-risk cohort, the proportion of stillbirths and neonate deaths being at 53% and 47%, respectively.
These findings suggest that if all subjects were delivered by the end of the 39th week (38 +6 ), there would be 33% less intrauterine deaths with the cost of only 11% more neonatal deaths, resulting in an overall 18% reduction of total losses, whereas delivery at 39 weeks (39 +0 to 39 +6 ) would result in only 911 more losses (14,580 vs 13,669, +7%), compared with delivery at 38 completed weeks.
The authors suggest that the best gestational age for delivery in singleton low-risk pregnancies is before 39 weeks’ gestation, but this applies to this specific cohort, which is characterized by an overall double number of intrauterine deaths, in comparison with the neonatal deaths (10,863 vs 5776). In another pregnant population with a higher ratio of stillbirths to neonatal deaths (eg, high-risk pregnancies of this cohort: 1912 vs 581), the optimal gestational age for delivery would be earlier and vice versa.
A more thorough consideration of this issue possibly would be the inclusion of infant deaths associated with each gestational week in the estimation of the risk of delivery; this would lead to moving the best week for delivery later in pregnancy, probably at 39 weeks’ gestation. The only undisputed finding of this study is that low-risk pregnancies should not progress beyond a specific point in the beginning of the 41st week of gestation because this would entail a continuous increase in both fetal and neonatal deaths.