Murphy et al. Maternal asthma is associated with reduced female fetal growth. Am J Respir Crit Care Med 2003;168:1317-23

Abstract

A low birth weight is more common in babies born to mothers with active asthma during pregnancy. This study investigated the patterns of such low birth weight and possible underlying mechanisms in a group of women with active asthma who were not treated with inhaled or systemic steroids during pregnancy in comparison with a control group of pregnant women. In pregnant women with asthma, there was a significant reduction in birth weights in female babies, whereas male birth weights were unaffected. The presence of a female fetus in these asthmatic women was associated with significantly reduced placental levels of 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2) activity and fetal estriol. 11β-HSD2 normally metabolizes maternal cortisol in the placenta, reducing the amount of cortisol reaching the fetus. This may explain the somewhat higher cortisol levels in the cord blood of the female babies born to the asthmatic women. The authors concluded that in pregnancies complicated by asthma there are fetal sex–specific adverse effects on placental function and female fetal growth that possibly explain the lower birth weight in female babies. It would be interesting to compare these findings with those in pregnant women whose asthma was not active.