MONTREAL, March 13 -- The gender of a fetus has no detectable significant effect on the risk of asthma exacerbations in pregnant women, researchers here said.

In a retrospective analysis of more than 5,500 pregnancies, gender also had no bearing on the mother's use of asthma medications, according to Lucie Blais, Ph.D., of the University of Montreal, and colleagues.

The finding contrasts with earlier -- but smaller -- studies that had hinted that women carrying girls were more likely to have asthma exacerbations, the researchers said in the January issue of Respiratory Medicine.

The study doesn't rule out a minor impact of fetal gender on maternal symptoms, the researchers said, but it "provides evidence that these changes are not serious enough to lead to a moderate to severe exacerbation," they argued.

So, physicians should aim at asthma control during pregnancy regardless of the gender of the fetus, Dr. Blais and colleagues said.

For the analysis, the researchers studied three large databases in the Canadian province of Quebec, which provided information on medical services, prescriptions, acute care hospitalizations, births, and stillbirths.

Through the linked databases, Dr. Blais and colleagues found a cohort of asthmatic women with 11,257 singleton pregnancies between 1990 and 2002, nearly equally split between female and male fetuses. Women could be included in the cohort more than once.

The researchers found:

* Among women carrying a girl, 15.3% had an exacerbation at any time during the pregnancy, compared with 15.1% of those carrying a boy. The difference was not significant.
* Differences were also not significant in any trimester.
* On average, the dose per week of short-acting beta-agonists was similar in each trimester and during the overall pregnancy, regardless of the gender of the fetus.
* The proportion of women who used at least one dose of a short-acting beta-agonist per week on average was 62.5% for those carrying a girl and 62.6% for those expecting a boy.
* Similar proportions of women in each group used inhaled corticosteroids in each trimester and during the entire pregnancy, where the rates were 41.6% for those carrying a female fetus and 41.0% for those with a male fetus.
* Daily steroid doses were also similar between groups.

Dr. Blais and colleagues found 1,674 women who had more than one pregnancy during the study period and, of those, 874 had both a boy and a girl.

But there was no significant difference in exacerbation rates associated with differences in fetal gender, they found.

The researchers said the medication data reflect dispensing and might not correspond exactly to use. Also, the outcome was evaluated for trimesters or the entire pregnancy, which may have missed some short-term changes in asthma control.

The researchers also did not have access to clinical data, which precludes evaluation of a mild lack of asthma control that might be perceived by the mother.

Primary source: Respiratory Medicine
Source reference:
Firoozi F, et al "Effect of fetal gender on maternal asthma exacerbations in pregnant asthmatic women" Respir Med 2009; 103: 144-151.