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However, the study did find a positive association between some rare birth defects and mothers with asthma, and potentially with their medication use. But, the researchers couldn't tease out whether the problem was a loss of oxygen from less than well-controlled asthma or an effect of medications.
"Worsening asthma is a risk to the mom and the fetus. Hypoxia (a lack of oxygen) we know is a problem for a developing fetus. And, the potential risk they found here is very small. Even if it turns out to be a true increase, the risk is so small. This study raises more questions than it answers," said Dr. Natalie Meirowitz, chief of the division of maternal fetal medicine at Long Island Jewish Medical Center in New Hyde Park, N.Y.
What's most important, she said, is that expectant mothers with asthma don't just stop their medications. "That's really a problem, and then they end up needing more medication," she said.
Findings from the study were published online Jan. 16, ahead of February print publication in Pediatrics.
Between 4 percent and 12 percent of expectant mothers have asthma, according to background information in the article. Current guidelines recommend that women keep taking their asthma medications during pregnancy.
There are two main types of asthma medications: bronchodilators (also known as rescue medication) and anti-inflammatories, which include inhaled and oral steroids, as well as several other medications. Anti-inflammatory medications are generally used long term to help control asthma symptoms.
For the study, the researchers compared nearly 2,900 infants born with birth defects to more than 6,700 babies born with no birth defects. Mothers of these infants were asked to recall their medication use one month before and during pregnancy.
For most birth defects, the researchers found no statistically significant associations between asthma medication use and the development of birth defects.
They did, however, find a positive association between asthma medication use and certain rare birth defects. The risk of isolated esophageal atresia -- an abnormality of the esophagus -- was more than doubled in women who used bronchodilators. The risk of isolated anorectal atresia -- a malformed anus -- was more than doubled with maternal anti-inflammatory use. And, the risk of omphalocele -- a defect in the abdominal wall -- was more than quadrupled for either type of asthma medication.
But, the authors wrote, the "observed associations may be chance findings or may be the result of maternal asthma severity and related hypoxia rather than the medication use."
They added that it's also important to keep these findings in context. The rate of these birth defects ranged from 1.2 to 4.6 per 10,000 births. So, even a four-fold increase in the risk of having one of these defects results in far less than a 1 percent chance for any individual woman and her child.
"As obstetricians, we need to pay attention to this, but it's really important to oxygenate mom. We really need to make sure that there's oxygen flowing freely between mom and baby," said Dr. Mary Rosser, an obstetrician with Montefiore Medical Center in New York City.
Also, Rosser pointed out that there was a lot that wasn't known about the expectant mothers. The authors weren't able to assess the severity of their asthma. They also didn't know anything about the medication doses.
Asthma expert Dr. Jennifer Appleyard agreed with Rosser and Meirowitz. "They really couldn't tease apart what was the medicine and what was the asthma," she said.
"You need to treat the asthma. There's more risk to uncontrolled asthma than a slight possible risk of a rare birth defect," said Appleyard, the chief of allergy and immunology at St. John Hospital and Medical Center in Detroit.
"No matter what type of patient you're treating -- expectant mom or not -- the goal is to treat patients with the minimum amount of medication necessary," she added.
Rosser and Meirowitz said that, ideally, women should visit their obstetrician/gynecologist before getting pregnant to review their medication use and to make sure that their asthma is well controlled.
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