Cohort study finds newborn respiratory complications less common when mothers of babies with fetal lung immaturity at 34–37 weeks’ gestation given antenatal steroids
- 1Perinatal Institute and Division of Neonatology, Cincinnati Children's Hospital Medical Center
- 2Center for Prevention of Preterm Birth, Perinatal Institute, Cincinnati Children's Hospital Medical Center
- 3Department of Obstetrics and Gynecology, University of Cincinnati College of Medicine
- Correspondence to: Dr Beena D Kamath-Rayne
Perinatal Institute, Cincinnati Children's Hospital Medical Center, MLC 7009, 3333 Burnet Avenue, Cincinnati, OH 45229, USA;
Commentary on: Yinon Y, Haas J, Mazaki-Tovi S, et al. Should patients with documented fetal lung immaturity after 34 weeks of gestation be treated with steroids? Am J Obstet Gynecol 2012;207:222.e1–4.
Implications for practice and research
Infants whose mothers were treated with antenatal corticosteroids (ANS) after documented fetal lung immaturity at >34 weeks’ gestation had a lower rate of composite respiratory morbidity.
There was no statistically significant difference in the rate of special care unit admission.
The study supports prolonging pregnancy as long as possible without incurring undue risk to the mother as the most beneficial approach to avoid prematurity-related newborn complications.
Late preterm infants are the fast-growing proportion of preterm infants in the USA, and these infants are at risk for a variety of prematurity-related morbidities, including respiratory and feeding difficulties and neonatal sepsis. While ample evidence supports the use of ANS to decrease respiratory distress syndrome (RDS) in infants born <34 weeks’ gestation, scarce data exist to support efficacy when administered in pregnancies delivered at >34 weeks’ gestation.
In this retrospective cohort study from Sheba Medical Centre, Israel, the authors studied mothers delivered at 34–37 weeks’ gestation after an amniocentesis documenting immature fetal lung indices (TDx-FLM II <50 mg/g). Infants of 83 mothers treated with ANS were compared to infants of 84 mothers who were not. The primary outcome was composite respiratory morbidity, including RDS, transient tachypnoea of the newborn (TTN), or need for respiratory support. The authors also compared differences in major maternal characteristics and other neonatal outcomes.
There was a lower incidence of respiratory support (8.4% vs 20%, p=0.03) and composite respiratory morbidity (8.4% vs 21%, p=0.02) in infants of ANS-treated mothers. The lower rate of admission to special care unit (17.0% vs 29% p=0.07) was not statistically significant. Multiple linear regression indicated that ANS administration, TDx-FLM II value and gestational age at delivery were significantly associated with composite respiratory outcome.
The authors have contributed to the body of evidence regarding the use of ANS in pregnancies >34 weeks gestation, although their findings are limited to pregnancies with immature fetal lung indices after amniocentesis. With the retirement of the most popular fetal lung maturity test, the FLM-TDx II (the test used in this study), the current methods of fetal lung maturity testing are imperfect in their prediction of respiratory morbidity. Several studies have shown that despite mature fetal lung indices, infants continue to have other respiratory and neonatal morbidities related to prematurity.1 Thus amniocentesis for this purpose is being performed with less frequency.
The more general question of whether ANS should be used in pregnancies at risk of delivery between 34 and 37 weeks’ gestation has not been answered. A Brazilian trial randomised women at imminent risk of delivery between 34 and 36 weeks to ANS versus placebo. There was no difference in the incidence of respiratory disorders (including RDS or TTN), nor the need for ongoing respiratory support.2 A recent retrospective study analysed clinical decision-making after amniocentesis with immature fetal lung indices ≥34 weeks’ gestation3 and found ANS-exposed infants did not have decreased rates of respiratory or other neonatal morbidity, yet had higher rates of hypoglycaemia and sepsis work-up. This indicates that the number needed to treat for harm may be less than the number needed to treat for benefit in infants >34 weeks.3
Stutchfield et al4 randomised women scheduled to deliver >37 weeks by caesarean to receive ANS versus placebo. Similar to the results of Yinon and colleagues, ANS-treated mothers had decreased incidence of RDS while frequency of admission to the special care unit was similar between groups, indicating that the infants likely had other prematurity-related complications needing advanced neonatal care. Therefore, decisions regarding delivery timing should be carefully weighed considering the risks to the mother and fetus of prolonging pregnancy and the risk to the neonate of early delivery, where morbidity related to immaturity of organ systems other than just the respiratory system may occur.