Pregnancy outcome after inadvertent ivermectin treatment during community-based distribution. Ivermectin is the drug of choice for community-based treatment of onchocerciasis. Since pregnancy testing during mass distribution campaigns is not feasible, the safety of ivermectin in pregnancy must be established. During a 3-year study, ivermectin was distributed to the population of a rubber plantation (14,000 people) in Liberia. Only 31% of women were aware of their pregnancy status during the first month; it was calculated that about half of women in the first trimester of pregnancy are likely to be treated inadvertently. 203 children born to women inadvertently treated during pregnancy were identified. In this limited sample, there was no significant difference in birth defects between treated and untreated mothers in the same population or compared with a reference population. Children of treated and untreated mothers showed no difference in developmental status or disease patterns. Further surveillance is necessary; however, since no major effects of ivermectin on pregnancy outcome were detected, there seems no need to change existing strategies of ivermectin distribution. 