For the hundreds of millions of women living in regions where ivermectin mass drug administration campaigns run annually, the question of what happens when conception coincides with treatment has lacked rigorous human data — until now. Animal toxicology flagged teratogenic signals at supratherapeutic doses decades ago, creating a precautionary cloud over inadvertent early-pregnancy exposures. These African trial data begin to lift that cloud with real-world human evidence.

The BOHEMIA program embedded a nested prospective cohort sub-study within two large cluster-randomized trials — one in Mopeia, Mozambique (mid-2022) and one in Kwale, Kenya (late-2023) — delivering three monthly rounds of ivermectin at 400 mcg/kg versus albendazole 400 mg fixed-dose for malaria transmission reduction. Women aged 13–49 who became pregnant within a window spanning two weeks before to four weeks after drug exposure were enrolled, excluded from further dosing, and followed monthly through delivery. The primary endpoint was incidence of adverse pregnancy outcomes, capturing a composite relevant to fetal and maternal safety at population scale.

The finding that inadvertent periconceptional ivermectin exposure did not produce a clear increase in adverse pregnancy outcomes matters beyond these two sites. Ivermectin has now reached over 5.9 billion cumulative treatments through onchocerciasis and lymphatic filariasis elimination programs — populations where pregnancy detection at the moment of mass drug administration is practically impossible. Prior pharmacovigilance data from these campaigns had hinted at safety, but those signals were largely passive and underpowered. A prospectively designed, assessor-blinded sub-study nested within randomized infrastructure is substantially more credible. Key limitations include the observational nature of the sub-study itself (women were not randomized to exposure), reliance on self-reported last menstrual period for conception timing, and a sample size constrained by the narrow periconception enrollment window. This is confirmatory and reassuring for program planners, though not sufficient to establish formal regulatory safety clearance for intentional use in early pregnancy.