Pregnant women infected by the Zika virus: Ultrasound findings and growth patterns of fetuses with and without microcephaly.

Objective: To compare ultrasound growth measurements of fetuses with and without microcephaly in suspected Zika virus infection.

Methods: A retrospective cohort study included pregnant women with suspected Zika virus infection to evaluate 110 fetuses with and without microcephaly. The women had been admitted to the fetal medicine unit between October 2015 and August 2016. Cases of fetal microcephaly resulting from other causes were excluded. Variables evaluated were the ultrasound measurements taken at fetal biometry. The relation between each fetal biometry measurement and gestational age was analyzed using fractional polynomials in random-effects regression models. To evaluate fetal growth, curves of the mean fetal biometric parameters were constructed as a function of gestational age.

Results: Mean biparietal diameter and mean head circumference increased in both groups as a function of gestational age. In the group with fetal microcephaly, mean head circumference was significantly larger in the 13th and 14th weeks of pregnancy, becoming smaller compared with the group without microcephaly from the 20th week onwards, with the difference increasing with gestational age.

Conclusion: Fetal head circumference continues to increase until birth, even after a diagnosis of microcephaly, with a reduction only in the pace of growth. Growth decelerates as the pregnancy approaches term.