Women who have an asthma attack during the first three months of pregnancy put their babies at a greater risk of birth defects than asthmatic mothers who did not have a flare-up during that period, a new Canadian study shows.
The research, published in next month's issue of the Journal of Allergy and Clinical Immunology, found that women who had uncontrolled asthma during this crucial period in fetal development were 48 per cent more likely to have a baby with at least one birth defect compared with those who were taking their medication.
"I hope it will encourage women to continue their treatment during pregnancy. This gives some evidence that stopping your treatment and then being more at risk of having an asthma attack puts your baby at risk of having a congenital malformation," Lucie Blais, an associate professor in pharmacy at the University of Montreal and lead author of the study, said in an interview yesterday.
Prof. Blais said it has long been suspected that an asthma attack during pregnancy can cause birth defects. But literature on this topic is rare.
The study analyzed more than 4,300 pregnancies in Quebec through health-care and pharmacy records.
The researchers found that the rate of birth defects among the children with mothers who had an asthma exacerbation was 12.8 per cent, compared to 8.9 per cent for pregnant women with controlled asthma during the first trimester.
The rate of birth defects in the general population is anywhere between 3 to 6 per cent, Prof. Blais said.
She explained that birth defects can be more common because when a pregnant woman has difficulty breathing, both mother and fetus can see a drop in the level of oxygen in their blood. A baby, especially in the early stages, needs a consistent supply of blood for normal growth and survival.
"If you take moderate doses of inhaled corticosteroids, which is the medication that they should take to control their asthma ... this will reduce the risk of having an asthma attack and then reduce the risk of having a malformation," Prof. Blais said.
"They should take their medication as prescribed, as usual."
The most frequent birth defects were musculoskeletal and cardiac, the researchers found.
Malcolm Sears, research director at the Firestone Institute of Respiratory Health in Hamilton and an asthma epidemiologist, said the study reinforces what doctors have been telling asthmatic pregnant women for some time now. He said that there is a tendency among patients to dispense with all medication during pregnancy, sometimes with good reason. But the safety of medication used for asthma is well known.
