Adverse pregnancy outcomes according to gestational age of ZIKV maternal infection
Of the 92 women with ZIKV infection in the first trimester, 35.9% had an adverse pregnancy outcome versus 2.8% and 1.9% in the second and third trimesters, respectively (Table 2). Most (76.7%) of adverse pregnancy outcomes potentially related to ZIKV occurred when the infection was acquired during the first trimester.
Importantly, only one of the seven infants whose mothers had ZIKV infection beyond the first trimester (14 weeks) was classified as typical CZS phenotype. Three of the remaining infants were intrauterine growth restricted what could be related to the moderate microcephaly in whom no brain abnormalities were detected. Two had been congenitally infected with CMV, probably explaining their brain imaging findings, and one had clinical and imaging findings of a possible inborn error of metabolism. None of these infants had positive ZIKV results. These 5 infants with other plausible causes for the observed postnatal CNS anomalies were excluded from the typical CZS phenotype classification.
The gestational age of ZIKV infection that best predicted adverse outcomes was 11 completed weeks of pregnancy (Figure 2). The relative risk of adverse pregnancy outcomes potentially related to ZIKV infection was 14.0[95%CI:7.6-26.0] for maternal infection acquired< 11 weeks as compared to more advanced gestational ages. Gestational age less than eleven completed weeks (11.9) was also the best predictor of the typical CZS phenotype with brain abnormalities. These were much more likely to occur with maternal infection < 11 weeks of gestation than afterward (relative risk=76.2[95%CI:10.1-576.6]).