Microcephaly and Associated Risk Factors in Newborns: A Systematic Review and Meta-Analysis Study

Congenital microcephaly is caused by a multitude of drivers affecting maternal–fetal health during pregnancy. It is a rare outcome in high-income industrial countries where microcephaly rates are in the range of 0.3–0.9 per 1000 newborns. Prevalence of microcephaly varies considerably across developing countries and can go as high as 58 cases per 1000 live births in pregnancies exposed to infection by Zika virus (ZIKV). Not only ZIKV-infected pregnancies, but other drivers can modulate the occurrence and severity of this outcome. Here, we sought to test the ZIKV–microcephaly association vs. competing hypotheses using a meta-analysis with 8341 microcephaly cases pooled from 10,250,994 newborns in the Americas, Africa, and Asia. Analysis of risk ratios (RR) showed teratogens the most likely microcephaly-associated risk factor (RR = 3.43; 95%-CI 2.69–4.38; p-value < 0.0001), while the statistical significance of the ZIKV–microcephaly association was marginal (RR = 2.12; 95%-CI 1.01–4.48; p-value = 0.048). Other congenital infections showed strong but variable associations with microcephaly (RR = 15.24; 95%-CI 1.74–133.70; p-value = 0.014). Microcephaly cases were associated with impoverished socioeconomic settings, but this association was statistically non-significant (RR = 2.75; 95%-CI 0.55–13.78; p-value = 0.22). The marginal ZIKV–microcephaly association and statistical significance of the competing hypotheses suggest maternal ZIKV infection might not be a cause of microcephaly alone.