(Reuters Health) - Pregnant women who take fluconazole, an oral antifungal used to treat vaginal yeast infections, may be more likely to have miscarriages than women who don’t take this pill during pregnancy, a Canadian study suggests.

About one in 10 pregnant women develop yeast infections, a risk that is up to 10 times higher than in nonpregnant women, researchers note in CMAJ. While topical medicines are usually the first thing prescribed for yeast infections, women who don’t improve with this approach may be given fluconazole even though using this drug in pregnancy has been linked to an increased risk of certain birth defects including skeletal and heart malformations.

For the current study, researchers examined data on 29,458 pregnancies ending in miscarriage between 6 and 19 weeks gestation and on 245,059 pregnancies that didn’t end in miscarriage.

Women who took low doses of fluconazole (150 milligrams) were more than twice as likely to have a miscarriage as women who didn’t use this drug at all during pregnancy, and women who took higher doses of the drug had more than triple the miscarriage risk.

“Regardless of dosage, oral fluconazole use is associated with the risk of spontaneous abortions,” said lead study author Anick Bérard of the University of Montreal in Quebec.

The drug wasn’t associated with an increased risk of stillbirth, however, and only high doses were linked to heart defects, Bérard noted.

“This is reassuring given that low-dose is the most frequently used,” Bérard said.

About 70 percent of the patients who received fluconazole during pregnancy received a low dose of the drug, the study found.

All of the women in the study were pregnant in Quebec between 1998 and 2015.

Overall, the risk of miscarriage was higher when women were older, smokers, or drinkers, and lower when women took folic acid starting at least six months before pregnancy.

One limitation of the study is the possibility that researchers lacked data on all of the women who smoked or drank or took folic acid, the study authors note. They also didn’t have lab test results confirming that women had yeast infections when they were prescribed fluconazole.

The estimated risk of miscarriage associated with the drug may also be low because the analysis only included miscarriages that were diagnosed by clinicians, and many women who miscarry early in pregnancy may not necessarily have this event detected or diagnosed by a doctor.

Still, the results underscore the importance of pregnant women seeking alternatives to oral fluconazole for yeast infections, said Dr. Vanessa Paquette, coauthor of an accompanying editorial and a pharmacy researcher at the University of British Columbia in Canada.

“The recommended treatment of choice in pregnancy for vaginal yeast infections are topical antifungal agents (clotrimazole, miconazole) that are administered via the vagina in the form of cream or vaginal tablet,” Paquette said by email. “These agents have been shown to be safe and effective in pregnant women.”

Even though oral fluconazole is available on drugstore shelves without a prescription, “oral fluconazole treatment for vaginal yeast infections in pregnant women should be avoided at this time,” Paquette added.

SOURCE: bit.ly/2XfFTAy CMAJ, online February 19, 2019.