Antenatal corticosteroids for preterm birth: dose-dependent reduction in birthweight, length and head circumference

Aim: This study was undertaken to evaluate the effects of repeated courses of antenatal corticosteroids (ACS) on foetal growth. Methods: We studied 94 infants exposed to 2–9 courses of ACS. Mean gestational age (GA) at first exposure was 29 and at birth 34 weeks. Exposure data were retrieved from case record files. Information on potential confounders was collected from the Swedish Medical Birth Registry. Standard deviation scores (SDS) for birthweight (BW), birthlength (BL) and head circumference (HC) were calculated and considered as outcomes. Results: GA at start of ACS did not affect outcome. BW‐SDS, BL‐SDS and HC‐SDS were ?0.21, ?0.19 and +0.25 in infants exposed to two courses, compared to ?1.01, ?1.04 and ?0.23 in infants exposed to ≥4 courses of ACS (p = 0.04–0.07). In multiple regression analyses, ≥4 courses were associated with lower BW‐SDS, BL‐SDS and HC‐SDS (p = 0.007–0.04) compared to SDS after 2–3 courses. The effects from ≥4 courses on BW and BL were comparable to reduction in birth size seen in twins and on HC to that observed after maternal smoking. Conclusions: Multiple courses of ACS are associated with a dose‐dependent decline in foetal growth, which may affect later development and health.