Fever in pregnancy and offspring head circumference

To examine whether maternal fever during pregnancy is associated with reduced head circumference and risk of microcephaly at birth.

A prospective study of 86,980 live-born singletons within the Danish National Birth Cohort was carried out. Self-reported maternal fever exposure was ascertained in two interviews during pregnancy and information on head circumference at birth was extracted from the Danish Medical Birth Registry.

Fever in pregnancy was reported by 27% of the mothers, and we identified 3370 cases of microcephaly (head circumference less than or equal to third percentile for sex and gestational age) and 1140 cases of severe microcephaly (head circumference less than or equal to first percentile for sex and gestational age). In this study, maternal fever exposure was not associated with reduced head circumference (adjusted β = 0.03, 95% confidence intervals [CI]: 0.01-0.05), increased risk of microcephaly (odds ratio: 0.95, 95% CI: 0.88-1.03) nor severe microcephaly (odds ratio: 1.01, 95% CI: 0.88-1.15) in the offspring. These findings were consistent for increasing numbers of fever episodes, for increasing fever severity, and for exposure in both early pregnancy and midpregnancy.

In this most comprehensive study to date, we found no indication that maternal fever in pregnancy is associated with small head size in the offspring.