OEIS complex: Prevalence, clinical, and epidemiologic findings in a multicenter Mexican birth defects surveillance program.

The prevalence of OEIS in our sample is within the highest reported worldwide. First-trimester pregnancy maternal influenza infection and twining emerge as associated risk factors for OEIS. Although twin zygosity was not defined, the observed severest phenotypes in twins endorse the hypothesis that OEIS and monozygotic twinning are features of disturbances on early blastogenesis.