Zika-caused microcephaly takes many weeks to show up in prenatal neuroimaging

It takes at least 15 weeks for fetuses to develop signs of microcephaly or other problems observable on prenatal imaging after Mom is bitten by a Zika virus-carrying mosquito during her first trimester, according to the authors of a South American study published online in Obstetrics & Gynecology.

Based on this and other findings, lead author Miguel Parra-Saavedra, MD, director of maternal-fetal medicine at the Cedifetal Clinic in Barranquilla, Colombia, and colleagues urge serial head and brain ultrasound and MRI of fetuses suspected of having been exposed to the virus.

The researchers reviewed the cases of pregnant women referred to that clinic and one other in Colombia after the women presented with possible Zika virus infection or their babies-to-be had findings on amniotic fluid samples consistent with congenital Zika syndrome.

In subsequent weeks, the fetal patients were serially assessed with ultrasound, MRI and lab testing.

The researchers reviewed the results of the exams and also tracked perinatal outcomes.

In their study report, Parra-Saavedra et al. describe 17 cases of confirmed prenatal maternal Zika virus infection with adverse fetal outcomes.

Some 14 of the women had symptoms, which showed up at a median gestational age of 10 weeks (range 7 to 14 weeks).

The team’s key findings on Zika-caused fetal defects included:

• The median time between Zika virus symptom onset and microcephaly (head circumference less than three standard deviations below the mean) was 18 weeks (range 15 to 24 weeks).
• The earliest fetal head circumference measurement consistent with microcephaly diagnosis was at 24 weeks of gestation.
• The earliest sign of congenital Zika syndrome was talipes equinovarus, a twisted-foot defect, which in two patients was noted first at 19 weeks of gestation.

Common findings on fetal MRI were not only microcephaly but also ventriculomegaly, polymicrogyria and calcifications.

“Our analysis suggests a period of at least 15 weeks between maternal Zika virus infection in pregnancy and development of microcephaly,” the authors write, adding that their research “highlights the importance of serial and detailed neuroimaging.”