A retrospective study in French Polynesia (2013–2014) found a strong association between Zika virus (ZIKV) infection and microcephaly in newborns. Of 66% of the population infected with ZIKV, 7 out of 8 microcephaly cases occurred in the four months following the ZIKV outbreak. The study estimated that ZIKV infection during the first trimester of pregnancy increased the risk of microcephaly by 95 per 10,000 women, with a prevalence of 2 per 10,000 neonates. Models suggesting increased risk in later trimesters were not significantly worse than the first-trimester model. The study provides the first quantitative estimate of ZIKV's risk to fetal/neonatal microcephaly. It highlights the need for public health measures to protect pregnant women from ZIKV, as the virus can infect a large proportion of a population. The study also emphasizes the importance of further research to understand ZIKV's role in congenital abnormalities and to develop effective treatments and vaccines. The findings support the need for prompt action to prevent microcephaly and other complications linked to ZIKV.A retrospective study in French Polynesia (2013–2014) found a strong association between Zika virus (ZIKV) infection and microcephaly in newborns. Of 66% of the population infected with ZIKV, 7 out of 8 microcephaly cases occurred in the four months following the ZIKV outbreak. The study estimated that ZIKV infection during the first trimester of pregnancy increased the risk of microcephaly by 95 per 10,000 women, with a prevalence of 2 per 10,000 neonates. Models suggesting increased risk in later trimesters were not significantly worse than the first-trimester model. The study provides the first quantitative estimate of ZIKV's risk to fetal/neonatal microcephaly. It highlights the need for public health measures to protect pregnant women from ZIKV, as the virus can infect a large proportion of a population. The study also emphasizes the importance of further research to understand ZIKV's role in congenital abnormalities and to develop effective treatments and vaccines. The findings support the need for prompt action to prevent microcephaly and other complications linked to ZIKV.