We read with great interest the editorial by Towers, et al regarding amniocentesis for fetal lung maturity (FLM) testing in the late preterm period for delivery planning. We had 3 concerns with the authors’ argument.

First, although the authors discussed respiratory distress syndrome (RDS) and common short-term morbidities in the newborn period, they failed to mention the significant long-term risks associated with late preterm birth, including increased infant mortality and impaired neurodevelopment, consequences commonly underestimated by obstetricians. Of note, the 34 week brain is only 65% of term brain weight and volume, making the late preterm period a time of critical importance in neurodevelopment. Increasing evidence supporting these risks should be weighed in decisions regarding delivery timing.

Second, the authors do not report the weaknesses of FLM testing, apart from the fact that lung maturity is not equivalent to overall maturity. Amniotic fluid FLM testing has high negative predictive value for postnatal absence of RDS; however, approximately 50% of infants with immature FLM testing do not have RDS. Further, RDS risk can be as high as 8% in 34 week newborns despite mature FLM testing, indicating substantial opportunity exists for improving FLM testing.

Finally, the authors state that antenatal corticosteroids (ANCS) followed by delivery for immature FLM indices is a possible treatment option. We feel clinical equipoise remains regarding benefit of ANCS administration after 34 weeks gestation. Our previous work evaluated outcomes of infants who received ANCS after immature fetal lung indices and were subsequently delivered within 1 week. Compared with expectant management with later delivery or waiting until mature FLM testing, respiratory morbidity was highest following ANCS administration and delivery than with the other management approaches. Furthermore, infants with immature FLM followed by ANCS and delivery had higher rates of hypoglycemia and sepsis evaluation, indicating this approach may incur some newborn risk. Even if ANCS were effective to reduce RDS risk at later preterm gestational ages, considering a baseline risk of RDS of 15% in newborns greater than 34 weeks’ gestation, the number needed to treat is quite high, approximately 145 to prevent 1 case of RDS. The Maternal-Fetal Medicine Units Network ALPS trial is underway to assess the benefit of ANCS administration at >34 weeks. Considering the unknown risk-benefit ratio of ANCS following immature FLM testing for delivery planning purposes, we urge caution with this practice until clinical trial results are available.