Vol. 18 •Issue 11 • Page 19
Carrying Female Fetus May Exacerbate Mother’s Asthma
ORLANDO, Fla.—Pregnant women with asthma who carry female fetuses are much more likely to suffer a worsening of their asthma symptoms, especially nighttime breathing problems, than those carrying male fetuses, according to Australian researchers.
The female fetus may produce a substance in response to the inflammation of an asthmatic mother’s airways that exacerbates asthma. But this is conjecture.
“Asthma is one of the most common medical problems complicating pregnancy,” lead author Peter Gibson, MBBBS, told a press conference at the American Thoracic Society meeting held here last year. “In one-third of women who have asthma, it gets worse during pregnancy; in one-third, it gets better; and in one-third, it stays the same.”
Apparently, most moms-to-be who fall in that unlucky one-third with worsening symptoms are carrying girls.
In earlier research, Gibson et al. showed that if an asthmatic woman were carrying a girl and the mother was not taking steroids, her baby would be of low birth weight. But the same didn’t hold true for boys.
“So in this study we asked: What impact did the sex of the baby have on the mom’s asthma?” explained Gibson, of the Department of Respiratory and Sleep Medicine for John Hunter Hospital, Newcastle, New South Wales, Australia.
They found that asthmatic mothers pregnant with baby girls tended to have worse symptoms than asthmatic mothers carrying boys. “Their lung function was reduced in the last trimester, and they needed more doses of steroids,” Gibson said. “We think the mechanism is inflammation. Our research now is to determine where that inflammatory effect is coming from and what it is.”
Counts of monocyte, a large, phagocytic white blood cell, were elevated in mothers of girls as opposed to boys, he said. As in the previous study, steroids helped ensure normal birth weight in the baby girls.
When each woman delivered, her asthma returned to its previous level.
The researchers studied a total of 151 pregnant women (80 with asthma who took inhaled glucocorticosteroids every day during pregnancy, 38 women asthmatic women who did not and 33 non-asthmatic pregnant women who served as controls).
They found that 60 percent of asthmatic women carrying male fetuses were symptom-free throughout their pregnancies and did not report nighttime breathing problems from the 18th to the 30th week of pregnancy. Among asthmatic women carrying girls, however, 61 percent were symptom-free at 18 weeks; but by the third trimester, that percentage had shrunk to just 28 percent.
“It’s a small population, but the effect was large,” Gibson said.
Gibson noted further that connective tissue diseases like rheumatoid arthritis and lupus tend to ease during pregnancy, but asthma worsens when the baby is female. Yet asthma and arthritis both have inflammatory components and both cause the body to produce T-helper cells–TH2 cells to combat asthma and TH1 cells to fight arthritis.
“Boy fetuses seem to be insensitive to these effects,” he said. “In children, three times as many boys as girls have asthma. But in adults, it shifts to women. Something shifts it. Researchers think it is sex-hormone related. Either testosterone protects men from asthma or estrogen predisposes women to it. Not until they move past age 50 do levels even out between the sexes.”
He concluded that asthma education and close monitoring during pregnancy are important obstetric measures. “People should seek to control their asthma during pregnancy,” he said.
Gibson acknowledged that women in his study had poor asthma management skills. “Many of these women fell through the care net,” he said. “Few had written action plans. Cough, dyspnea and night-time symptoms all increased significantly in late termÉWe see many women stop their inhaled corticosteroid use once they learn they’re pregnant. We’re not sure how common this is.”
Gibson’s clinic employs a nurse educator to teach asthmatic women effective self-management.
Murphy V, Gibson P, Giles W, et al. Maternal asthma is associated with reduced female fetal growth. Amer J Resp Crit Care Med. (2003; 168:1317-1323).
You can reach Michael Gibbons at [email protected].