Effect of fetal sex on airway lability in pregnant women with asthma.

The authors investigated the association between sex of the fetus and maternal airway lability among pregnant women with asthma. Data were prospectively collected among 702 pregnant women with a diagnosis of asthma who were recruited in southern New England between 1997 and 2000 and followed through pregnancy. Peak expiratory flow lability, defined as percent daily maximum minus the minimum divided by the mean, was assessed at enrollment and at 21, 29, and 37 weeks' gestation. There was a -9.9 percent (95 percent confidence interval: -19.4, -0.4) difference in airway lability observed between women carrying female fetuses and those carrying male fetuses. This difference persisted throughout pregnancy. Among pregnant asthmatic women, carrying a female fetus is associated with worse maternal asthma, as assessed by greater airway lability, than is carrying a male fetus.