Congenital cytomegalovirus (cCMV) is a condition that occurs in infants before birth. Most babies with cCMV don’t have health problems, but they are at a higher risk of microcephaly, a condition in which the head is smaller than normal. This study aims to evaluate the prevalence of microcephaly in infants with cCMV.

This population-based cohort study included a pooler cohort of 2,338,580 pregnancies. Exposure to cCMV in infants was documented in inpatient or outpatient records. The primary objective of this study was the prevalence of microcephaly, and the association of microcephaly with cCMV estimated using prevalence ratios (PRs).

Of 2,338,580 pregnancies, 336 infants (0.014%) were diagnosed with cCMV. The prevalence of microcephaly was 655 per 10,000 live births among patients with cCMV, as compared with 2.8 per 10,000 births in patients without cCMV. Further corrections suggested that the PR for microcephaly among infants with cCMV was 15. Corrected analysis after comparison with an unbiased sample of infants confirmed that the prevalence of cCMV in overall infants with microcephaly was 3.2%.

The research concluded that cCMV increased the prevalence of microcephaly by at least seven times in newborn infants. Therefore, the prevention of CMV infection during pregnancy is essential to reduce the number of newborns with microcephaly.