Conclusions and Comments

The number of pregnant women with laboratory evidence of possible recent Zika virus infection and the number of fetuses/infants with Zika virus–associated birth defects continues to increase in the United States. The proportion of fetuses and infants with birth defects among pregnancies with confirmed Zika virus infection at any time during pregnancy was more than 30 times higher than the baseline prevalence in the pre-Zika years, and a higher proportion of those with first trimester infections had birth defects (4). Although microcephaly was the first recognized birth defect reported in association with congenital Zika virus infection, Zika virus–associated brain abnormalities can occur without microcephaly, and neuroimaging is needed to detect these abnormalities (9). Neuroimaging is also used in other congenital infections to identify brain abnormalities; for example, neuroimaging findings in infants with congenital cytomegalovirus infection are correlated with neurodevelopmental outcomes (10). Postnatal neuroimaging is recommended for all infants born to women with laboratory evidence of Zika virus infection to identify infants with brain anomalies that warrant additional evaluation to ensure that appropriate intervention is provided (8). Based on data reported to the USZPR, the majority of these infants had not received recommended neuroimaging. In addition to infants with birth defects, complete follow-up and routine developmental assessment of all infants born to women with laboratory evidence of possible recent Zika virus infection is essential to help identify future outcomes potentially associated with congenital Zika virus infection and ensure that the referrals to appropriate support and follow-up care are made.

The findings in this report are subject to at least four limitations. First, selection bias might affect which pregnancies are reported to the USZPR, because pregnant women with symptoms of Zika virus disease might be more likely than asymptomatic women to be tested. Pregnant women with Zika virus exposure and prenatally detected fetal abnormalities or infants with birth defects might be more likely to be tested for Zika virus infection. In addition, pregnancies resulting in a loss might be more likely to have had a confirmed Zika virus infection and more likely to have the placenta or other pathologic specimens tested (11). However, it is also possible that birth defects in pregnancy losses, including stillbirths, have not been reported. Second, while CDC has worked closely with state and local health departments to obtain complete information, delays in reporting postnatal neuroimaging or infant Zika virus testing results are possible. In addition, some of the pregnancies included in the analysis were completed before CDC’s most recent infant guidance (8) was released, and thus, current recommendations for neuroimaging or testing might not have been implemented. Third, current testing methodologies are limited in that they can only identify recent Zika virus infections (5) and might miss those women who are tested when Zika virus RNA and/or IgM is no longer detectable; these pregnancies would not be included in the USZPR unless the fetus/infant or placenta has a positive Zika virus test result. Also, serologic testing cannot readily discriminate between flaviviruses because of crossreactivity (5); therefore, some pregnancies in the USZPR might have had a recent infection with a flavivirus other than Zika virus which could lead to an underestimate of the proportion of fetuses/infants affected. For this reason, in this report, analysis of the subset of pregnancies with laboratory-confirmed recent Zika virus infection was included. Finally, limited data are available about other maternal risk factors for birth defects, including genetic or other infectious causes, which might be causal factors for a few of the birth defects reported here.

These findings underscore the serious risk for birth defects posed by Zika virus infection during pregnancy and highlight why pregnant women should avoid Zika virus exposure and that all pregnant women should be screened for possible Zika virus exposure at every prenatal visit, with testing of pregnant women and infants in accordance with current guidance (https://www.cdc.gov/zika/pdfs/zikapreg_screeningtool.pdfCdc-pdf ) (8,12). Zika virus testing of infants is recommended for 1) all infants born to women with laboratory evidence of Zika virus infection in pregnancy and 2) infants with findings suggestive of congenital Zika syndrome born to women with an epidemiologic link suggesting possible transmission, regardless of maternal testing results. Infants without abnormalities born to women with an epidemiological link suggesting possible Zika virus exposure during pregnancy, and for whom maternal testing was not performed or was performed more than 12 weeks after exposure, should have a comprehensive exam. If there is concern about infant follow-up or maternal testing is not performed, infant Zika virus testing should be considered. The initial evaluation of infants should include a comprehensive physical examination, including a neurologic examination, postnatal neuroimaging, and standard newborn hearing screen. Additional evaluation might be considered based on clinical and laboratory findings, however routine developmental assessment is recommended as part of pediatric care (8). Based on initial USZPR reports, most infants born to women with laboratory evidence of possible recent Zika virus infection during pregnancy might not be receiving the recommended evaluation (e.g., postnatal neuroimaging). CDC is working with public health officials, professional societies, and health care providers to increase awareness of and adherence to CDC guidance for the evaluation and management of infants with possible congenital Zika virus infection. Identification and follow-up care of infants born to mothers with laboratory evidence of possible recent Zika virus infection during pregnancy and infants with possible congenital Zika virus infection can ensure that appropriate intervention services are available to affected infants.