Objective To analyze adverse fetal and neonatal outcomes of Zika virus infection by the timing of infection during pregnancy. Method: Cohort study of 190 pregnancies with 193 offspring with a positive RT-PCR test for Zika virus (March/2016 to April/2017). Results Death or defects related to congenital Zika virus infection were identified in 37.3% of fetuses and newborns, and microcephaly in 21.4% of the newborns. The proportion of small for gestational age newborns was 21.9%. Maternal symptoms in the first trimester were significantly associated with the birth of newborns with microcephaly/cerebral atrophy, small for gestational age and with the deaths (one abortion, one stillbirth and the two neonatal deaths). Maternal infection during the second trimester was further associated with asymptomatic newborns at birth. The study showed that 58.5% of the offspring with microcephaly and / or cortical atrophy were small for gestational age, with an evident decrease in symptomatic offspring without microcephaly, 24.1%, and with only 9.1% in the asymptomatic group. Conclusion This study showed that the earlier the symptoms appear during gestation, the more severe the endpoints. We found a higher percentage of small for gestational age newborns exposed to Zika virus early in gestation. We also found a group of apparently asymptomatic newborns with proven Zika infection, which highlights the importance of follow up studies in this population. Author summary Zika virus infected pregnant women brought many challenges for the public health system because at the beginning of the outbreak there was no knowledge of the consequences of this disease. Microcephaly became the more common and threatening finding related to intrauterine Zika virus infection. Moreover, it was observed that there were others serious consequences of this disease during pregnancy, which were a burden for mothers and children. This study, following infected pregnant women, referred to our institution, enabled the medical professional team to improve their expertise in dealing with this new disease. Ours results showed a high frequency of intrauterine growth restriction, with babies being born small. Besides, it was found that the more severe cases occurred in women who were infected during the first trimester of gestation. Infections during the last half of the gestation more frequently leaded to babies born without symptoms. However, these results highlight the importance of following the babies born apparently asssymptomatic.
