Babies born to women who take corticosteroid drugs for asthma or other chronic ills may not have a heightened risk of birth defects known as oral clefts, a study published Monday suggests.

“No drug can be proven 100 percent safe,” lead researcher Dr. Anders Hviid, of the Statens Serum Institute in Copenhagen, told Reuters Health by email. “However, our study supports that moderate to large increases in cleft risk can be excluded.”

“This should reassure pregnant women and women planning a pregnancy,” he said.

Researchers found that among more than 800,000 babies born in Denmark, there was no clear link between mothers’ use of corticosteroids early in pregnancy and the risk of oral clefts.

The findings do not prove there is no risk, experts say, but they should offer women some reassurance about their needed medications.

Oral clefts, including cleft lip and cleft palate, are among the most common type of birth defect, affecting about 6,800 U.S. infants each year. They arise when the tissues that form the roof of the mouth and the upper lip fail to fuse properly, at some point between the fifth and ninth week of pregnancy.

The causes of oral clefts are not entirely clear, but a combination of genetic predisposition and environmental factors seems to be at work.

Some research has implicated corticosteroid medications, which are widely used for asthma, eczema, other allergies and autoimmune diseases like rheumatoid arthritis and multiple sclerosis. Animal studies have suggested that the drugs can cause oral clefts, but whether that’s true of humans has remained unclear.

The findings, which appear in the Canadian Medical Association Journal (CMAJ), are based on data from all births in Denmark between 1996 and 2008.

Among 832,636 births, there were 1,232 cases of cleft lip or cleft palate. Overall, 6 percent of mothers used corticosteroids during the first trimester - either topical, inhaled, oral or nasal-spray forms.

The researchers found no evidence that corticosteroid use, in general, was linked to an increased risk of oral clefts.

When they looked at the different forms of the medications, there was an association between topical corticosteroids - used for skin conditions like eczema - and oral clefts.

But, the researchers say, that appeared to not be a true link, but an “artifact” of the way their statistical analysis was done. Hviid also pointed out that topical corticosteroids are among the least potent forms, so “the finding did not make any sense from a biological standpoint.”

Dr. David Beuther, a pulmonologist at National Jewish Health in Denver, agreed that the findings are reassuring.

“It goes along with what we’ve thought about the safety of steroids,” said Beuther, who was not involved in the study.