We read with interest the article “The risk of fetal death: current concepts of best gestational age for delivery” by Mandujano et al. We would like to comment on the interpretation of the risk of fetal death, calculated as a cumulative incidence (number of cases divided by the number of women during a given follow-up period) up to 42 weeks.
Using the cumulative incidence until 42 weeks shows a higher risk of stillbirth at 34 than at ≥40 weeks, because the risk calculation at 34 weeks takes into account deaths that occur at 42 weeks, almost 2 months later. In contrast, the rate of stillbirths (number of cases divided by the number of ongoing pregnancies in a given week) is low between 34-39 weeks, whereas it increases at term, particularly >42 weeks.
Reporting the risk of stillbirth until 42 weeks gives a prospect that does not reflect obstetrical reality: it calculates the risk in case of nondelivery and without any interval risk evaluation or intervention. Obstetric care consists in regular evaluation of the pregnant woman, especially near and beyond term. At each visit, the risk of stillbirth until the next visit should be balanced with the risk of neonatal mortality or morbidity in case of delivery. Decision of induction of labor or expectant management should be taken according to the risk-benefit assessment, ideally based on results of randomized trials.
We recalculated fetal and neonatal mortality, using data reported by Mandujano et al, as the risk of mortality during the interval until the next visit. We used the following schedule: a visit at 34, 38, 40, 41, and 42 weeks for the low-risk cohort, and at 34, 36, 38, 40, 41, and 42 weeks for the high-risk cohort. Using a different frequency of visits will give similar results. This approach shows that in an uncomplicated pregnancy the risk of stillbirth exceeds the risk of neonatal death >41 weeks ( Figure 1 ). In the high-risk cohort, as the one defined by the authors, the same would occur at 38 weeks ( Figure 2 ). This is in agreement with the results of randomized trials.