Ivermectin Taken at the Start of Pregnancy is Not Associated With An Increased Risk of Adverse Pregnancy Outcomes

A study led by the Barcelona Institute for Global Health (ISGlobal), an institution supported by the ”la Caixa” Foundation, found no increased risk of miscarriage, stillbirth or major congenital anomalies among women inadvertently exposed to ivermectin during the period from two weeks before conception to the first four weeks of pregnancy. The findings, published in eClinicalMedicine, add to the available evidence on the safety of this antiparasitic drug during the very early stages of pregnancy, although the researchers stress that the number of cases remains too small to warrant changes to current recommendations.

Ivermectin is one of the most widely used antiparasitic drugs worldwide and is administered through mass drug administration campaigns to control neglected tropical diseases. Although it has shown potential to reduce malaria transmission by killing the mosquitoes that spread the disease, its use during pregnancy remains contraindicated because of the limited evidence available in humans.

Each year, inadvertent exposure to ivermectin occurs during very early pregnancy, as many women are still unaware that they are pregnant during the first few weeks. Despite this, evidence on its safety remains very limited, particularly during the first trimester. To generate new data, the research team analysed a prospective cohort embedded within the BOHEMIA trials, conducted in Mozambique and Kenya to evaluate the impact of mass ivermectin administration on malaria transmission.

“The substudy included 238 women who became pregnant between two weeks before and four weeks after receiving ivermectin or albendazole, which was used as the comparator treatment. All participants were followed up monthly until the end of pregnancy,” explains Patricia Nicolas, first author of the study and an ISGlobal researcher at the time the research was conducted.

The largest cohort studied to date

Of the 238 women included in the study, 129 had been potentially exposed to ivermectin and 109 to albendazole. Among those with a known pregnancy outcome, adverse outcomes (miscarriage, stillbirth or major congenital anomalies) occurred in 22.9% of the group treated with ivermectin and 19.5% of the group treated with albendazole. The differences between the two groups were not statistically significant.

“This trial represents the largest prospective cohort published to date on exposure to ivermectin during the first weeks of pregnancy and complements the limited evidence available so far, which included fewer than one hundred documented first-trimester exposures,” says Nicolas.

Prenatal care: a key factor

In addition to the effect of treatment, the study showed that women who experienced adverse pregnancy outcomes were much less likely to have received antenatal care and recommended preventive measures during pregnancy, such as iron and folic acid supplementation, insecticide-treated bed nets and preventive treatment against malaria. However, it should be noted that women who experience very early miscarriages have fewer opportunities to attend antenatal care visits.

More evidence, but still not enough

“Our findings help strengthen the evidence base on inadvertent exposure to ivermectin in early pregnancy, but the number of documented pregnancies remains too small to support changes to clinical or regulatory recommendations. Further evidence from additional studies and surveillance systems will be needed,” concludes Carlos Chaccour, co-principal investigator of BOHEMIA and an ISGlobal researcher at the time of the study.

Reference
Nicolas, P., Mundaca, H., Brazeal, A., Houana, A., Ngama, M., Macucha, A., Matano, A., Elobolobo, E., Vegove, V., Martinho, S., Kariuki, M., Mbanze, J., Mitora, S., Montañà, J., Ringera, I., Túnez, L., Imputiua, S., Munguambe, H., Mutepa, V., … Chaccour, C. (2026). Risk of adverse pregnancy outcomes following inadvertent exposure to ivermectin during the periconception period: findings from two cluster-randomized trials in Mozambique and Kenya. eClinicalMedicine, 97(104069), 104069. https://doi.org/10.1016/j.eclinm.2026.104069