Objectives: to describe altered intrauterine ultrasound, analyze fetal head circumference (HC) growth and neonates' outcomes among presumed cases of congenital Zika syndrome in Brazil. Methods: 30 women were included in the study with suspected history of Zika virus (ZIKV) infection during pregnancy and fetal's brain altered on ultrasound diagnosis. Sociodemographic and obstetric characteristics, prenatal altered ultrasounds, HC and other perinatal outcomes have been described. The relation between HC and gestational age was analyzed by using random regression effects based on polynomials fractions. The Z test was calculated to determine an instant variant mean rate of the HC for each gestational age. Results: the mean gestational age of the ultrasound diagnosis was 33.3 + 4.7 weeks and HC at birth was 28.9 + 1.6 cm. The main altered brain ultrasound was microcephaly (96.7%). The analysis of the fetal head circumference showed an estimated increase of the average HC, as to gestational age, it did not occur in a linear form. The instant HC variation rate increased according to gestational age (p<0,001). Conclusions: Fetal's main morphological alteration was microcephaly, observing an increase in the head circumference according to gestational age in a non-linear form and the variation decreased with gestational age.

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.