Mother's asthma affects growth of fetus

Pregnant women with asthma are at risk for having a baby with reduced growth, but only if the mother is not treated with inhaled steroids and is carrying a girl. This holds true regardless of how severe the asthma is or whether the mother smokes.Researchers from John Hunter Hospital in Newcastle, Australia, based their study on 138 pregnant women with asthma and 44 pregnant control subjects. Steroid use throughout pregnancy was assessed in the asthma group, various hormone levels were determined at delivery and activity of an enzyme that prevents maternal levels of the hormone cortisol from reaching the fetus was determined. A reduction in female birth weights was only noted in asthmatic mothers who did not use inhaled steroids. Pregnancy with a female fetus was associated with an increase in maternal immune cells, reduced activity of cortisol, and an increase in fetal cortisol levels. By examining the endocrine and immune relationships between mother, placenta and fetus during asthmatic pregnancies, this study has provided strong evidence for a detrimental effect of maternal inflammation on placental function and female fetal growth and development.

The reduced growth seems to occur because some unknown factor produced by a female fetus increases inflammation in the mother. If not treated with inhaled steroids, this inflammation impairs the growth of the fetus. By contrast, pregnancy with a male fetus seems to have a weaker effect on maternal inflammation. This study provides evidence that in pregnancies complicated by asthma there is a fetal sex-specific effect on the maternal immune system with adverse effects on placental function and female fetal growth.