Zika virus is primarily transmitted through the bite of an infected Aedes species mosquito; however, it can also be spread by sexual transmission1,2 and vertically—from an infected pregnant woman.3,4The Colombian Instituto Nacional de Salud began official surveillance for symptomatic Zika virus disease in August 2015.5 By November 26, 2016, there were 19,448 pregnant women with symptomatic Zika virus disease reported to Instituto Nacional de Salud; most were not tested, but 5,882 had laboratory-confirmed Zika virus infection.
Although the natural history of congenital Zika virus infection is still under active investigation, the virus is an infectious teratogen that can cause significant neurologic sequelae and birth defects in neonates infected through maternal–fetal transmission.6,7 Congenital Zika virus infection is associated with fetal brain abnormalities including microcephaly.7,8 Previous reports have shown that these abnormalities, including microcephaly, ventriculomegaly, abnormalities of the corpus callosum, cortical migration abnormalities, and intracranial calcifications, can be detected by prenatal ultrasound examination.9–11 To identify abnormalities and monitor growth of fetuses whose mothers have laboratory evidence of Zika virus infection, the Centers for Disease Control and Prevention and Instituto Nacional de Salud recommended that for these women, ultrasound examinations every 3–4 weeks should be considered.12–14
The purpose of this report is to describe the timing of ultrasound findings consistent with congenital Zika syndrome after laboratory-confirmed maternal Zika virus infection.
MATERIALS AND METHODS
Between December 2015 and September 2016, two private perinatal referral clinics in Barranquilla and Ibagué, Colombia, provided care to pregnant women with laboratory-confirmed or suspected Zika virus infection. Women were included in this series if Zika virus RNA was detected by reverse transcription–polymerase chain reaction (RT-PCR) in either a maternal serum or urine sample, amniotic fluid, placenta, cord or neonatal serum sample, and if findings consistent with congenital Zika syndrome6 were present on fetal ultrasound examination or magnetic resonance imaging (MRI) (Sanz Cortez M, Yepez M, Zarutskie A, Castillo NA, Meza-Estrada V, Rivera-Casas A, et al. Fetal biometric assessment in a prospective cohort of 129 patients with clinical symptoms of Zika virus infection during pregnancy in Colombia. Ultrasound Obstet Gynecol 2016;48(suppl 1):51; Sanz Cortez M, Yepez M, Zarutskie A, Park N, Sharhan D, Castillo NA, et al. Fetal brain ultrasound findings in a prospective cohort of 129 patients with clinical symptoms of Zika virus infection during pregnancy in Colombia. Ultrasound Obstet Gynecol 2016;48(suppl 1):51.). These women were selected to focus on the measurement of fetal head circumference and other ultrasound parameters in pregnancies affected by congenital Zika syndrome. Medical records were abstracted by multiple staff members in each clinic to ascertain demographic characteristics such as maternal age and obesity (defined as body mass index [calculated as weight (kg)/[height (m)]2] 30 or greater), presence and timing of maternal or paternal Zika virus symptoms, maternal and neonatal laboratory results, prenatal ultrasound and MRI results, and perinatal outcomes. Maternal and neonatal Zika virus testing was performed at the central Public Health Laboratory in Bogotá5 using RT-PCR methods that have been previously described.15
Ultrasound examinations were performed using Voluson E8 Ultrasound. All images were reviewed to assess fetal brain anatomy and growth by at least two maternal–fetal medicine specialists who were aware of the women's Zika virus infection status. The first trimester was defined as less than 14 weeks of gestation. For the ultrasound measurements, microcephaly was defined as head circumference more than 3 standard deviations (SDs) below the mean for gestational age; for the postnatal measurements, the 3rd percentile for gestational age and sex was used, according to International Fetal and Newborn Growth Consortium for the 21st Century fetal growth standards.16 Fetal MRI was performed to better assess cortical development using a Philips Achieva 1.5-Tesla MRI system.
We describe characteristics of the pregnant women and report clinical details about the pregnancy, including delivery information. We report the timing and results of ultrasound and MRI examinations and compared ultrasound measurements with the International Fetal and Newborn Growth Consortium for the 21st Century fetal growth standards and postnatal sex-specific head circumference standards.17 This investigation was approved by the institutional review boards governing the two perinatal clinics. Informed consent for serial fetal imaging such as ultrasonography and magnetic resonance imaging was obtained from all study participants. Statistical analyses were performed using IBM SPSS Statistics 23.0. In accordance with U.S. federal human subjects protection regulations at 45 CFR §46.101c and §46.102d and with the Guidelines for Defining Public Health Research and Public Health Non-Research, the analysis of these data was reviewed by the human subjects protection coordinator at the National Center on Birth Defects and Developmental Disabilities of the Centers for Disease Control and Prevention and determined to be nonresearch, exempt from institutional review board evaluation.
We describe 17 cases of maternal prenatal Zika virus infection confirmed by RT-PCR with evidence of congenital Zika syndrome. The median maternal age was 23 years (range 16–31 years) and the median prepregnancy body mass index was 24.0 (range 17.3–32.8). First-trimester dating ultrasound information was available for 13 women (77%). Among the 14 symptomatic women, the median gestational age at onset of Zika virus disease symptoms was 10 weeks (range 7–14 weeks of gestation) (Appendix 1, available online at http://links.lww.com/AOG/A963). Of the three asymptomatic women, one had a partner with symptoms (fever, arthralgia, and rash) around the time of conception. This couple subsequently had sex without using condoms, making sexual transmission likely; amniotic fluid samples taken at 20 weeks of gestation were RT-PCR-positive for Zika virus. The other two asymptomatic women were diagnosed with Zika virus infection by the detection of Zika virus RNA in amniotic fluid at 28 and 33 weeks of gestation, respectively, after prenatal ultrasound findings were found to be suggestive of congenital Zika syndrome. For 10 women, all tested samples were positive for Zika virus infection by RT-PCR; the remaining seven women had both positive and negative samples (Appendix 1, http://links.lww.com/AOG/A963).
Most pregnancies had a full evaluation for other etiologies for birth defects to rule out other causes. All women had testing for other congenital infections; none of the tested samples had evidence of toxoplasmosis, syphilis, or herpes. Patient 7 had positive immunoglobulin G and immunoglobulin M for cytomegalovirus in maternal serum, although the amniotic fluid was negative for cytomegalovirus. Of the 15 neonates who had chromosomal analysis or karyotyping performed, 14 had normal results; patient 7 had a microduplication of chromosome 14q32, which was deemed to have no clinical relevance.
The median time between onset of Zika virus disease symptoms and the first nondating ultrasound examination was 8 weeks (range 3–20 weeks). For 15 of the 17 neonates, microcephaly was observed by prenatal ultrasound imaging. The median gestational age at which the head circumference was noted to be less than 3 SDs below the mean was 28 weeks (range 24–33 weeks of gestation). The median time from maternal report of Zika virus disease symptoms to ultrasound observation of microcephaly was 18 weeks (range 15–24 weeks). For three patients, earlier signs of congenital Zika syndrome were observed before the microcephaly diagnosis: talipes equinovarus (clubfoot) at 19.3 weeks for patient 7 and ventriculomegaly at 21.5 and 22.0 weeks for patients 13 and 3, respectively (Table 1). These defects are part of the congenital Zika syndrome phenotype and are likely a result of earlier brain damage. Patient 14 never received a microcephaly diagnosis, but this neonate had dysgenesis of the cerebellar vermis, which was the only sign of congenital Zika syndrome noted prenatally. Patient 16 had talipes equinovarus noted at 19.3 weeks of gestation and several brain abnormalities were observed at 21 weeks of gestation.
The serial prenatal ultrasound findings demonstrate fetal head circumference measurements relative to 3 SDs below the mean from the International Fetal and Newborn Growth Consortium for the 21st Century for the 13 patients with Zika virus symptoms in the first trimester (Appendix 2, available online at http://links.lww.com/AOG/A963). Ultrasound examinations performed between gestational weeks 20 and 24 did not show head circumferences below 3 SDs below the mean, whereas the next ultrasound examinations for these patients did. The timing of onset of Zika virus disease symptoms, positive laboratory RT-PCR results, ultrasound examinations, and observation of a fetal head circumference more than 3 standard deviations below the mean and the end of pregnancy are displayed for all 17 patients in Figure 1.
As part of the study protocol, fetal MRI was offered and performed in 16 patients (Table 1). The median gestational age at fetal MRI was 32.3 weeks (range 21–38 weeks of gestation). The MRI confirmed the ultrasound findings and provided additional information including nine cases with involvement of the corpus callosum. In six cases, there was evidence of polymicrogyria.
The median gestational age at birth was 38 weeks of gestation. For 6 neonates, the birth weights were below the 10th percentile according to International Fetal and Newborn Growth Consortium for the 21st Century standards.17 All 5-minute Apgar scores were 9 or 10. At delivery, the occipitofrontal circumference was less than the 3rd percentile for the 15 neonates who were prenatally diagnosed with microcephaly. The head circumference for case neonate 14, the neonate with dysgenesis of the cerebellar vermis, was just above the mean immediately after birth; however, when this neonate was seen 30 days after birth, the head circumference was more than 1 SD below the mean for age and sex.
This case series provides unique information on the trajectory of fetal head circumference after laboratory-confirmed maternal Zika virus infection for neonates eventually diagnosed with congenital Zika syndrome; at least 15 weeks elapsed from maternal Zika virus disease symptoms to the detection of fetal microcephaly with the earliest diagnosis of microcephaly occurring at 24 weeks of gestation.
Talipes equinovarus, the first sign for two patients, has been seen in previously reported Zika virus cases and might be the result of damage to the corticospinal tract or to the central or peripheral motor neurons.18 Other ultrasound findings included arthrogryposis, ventriculomegaly, intracranial calcifications, dysgenesis or agenesis of the corpus callosum, dysgenesis of the cerebellar vermis, and reduction in brain volume, which are consistent with a literature review of congenital Zika syndrome.6 Central nervous system anomalies were seen as early as 4 weeks after maternal infection in French Guiana, earlier than the 8 weeks we observed for ventriculomegaly in patient 13, indicating the brain is affected before microcephaly is observed.19
Limitations of this analysis include the fact that this was a convenience sample of women who sought care with these two clinics and that this was a retrospective analysis of available data for women mostly infected in the first trimester. Other limitations include the potential for error in the self-reported timing of Zika virus symptoms, error in head circumference measurements, and the fact that the number and spacing of ultrasound examinations for all included patients is not consistent as a result of the varying time of referral.
A summary of previous publications with information about the timing of prenatal diagnosis of microcephaly in pregnancies affected by Zika virus infection is consistent with the findings in our analysis (Appendix 3, available online at http://links.lww.com/AOG/A963). Of the 37 fetuses previously reported in the literature, the median gestational age when Zika symptoms (mostly rash) were observed in the pregnant woman was 10 weeks and the median gestational age at microcephaly diagnosis was 32 weeks. The median number of weeks between Zika virus symptoms and microcephaly diagnosis was 21 weeks (range 3–29 weeks) in these other reports. It should be noted that not all of the previously reported cases had laboratory-confirmed Zika virus infection and not all had serial ultrasound examinations, thus affecting the ability to diagnose microcephaly earlier in pregnancy.3,9,11,20–24 The variety of head circumference standards used and microcephaly definition (–3 SDs compared with the 3rd percentile) also make comparisons challenging.
This analysis of prenatal ultrasound and fetal MRI findings among a small case series of pregnancies affected by Zika virus infection can inform maternal–fetal medicine specialists who are managing pregnant women with Zika virus infection, including the more than 1,700 pregnant women with Zika virus infection who have been reported to the U.S. Zika Pregnancy Registry in the 50 U.S. states as of March 2017.25 It is important to note that among these 17 pregnancies, fetal microcephaly before 24 weeks of gestation was not observed, and no microcephaly was observed before 15 weeks had passed since Zika virus symptoms. This informs understanding of the natural history of perinatal Zika virus infection and cautions against falsely reassuring patients with normal ultrasound results within a few months from presumed maternal infection. It is important to continue monitoring pregnant women with serial ultrasound examinations. Continued transmission in subsequent seasons is anticipated; obstetric providers will need to continue to counsel pregnant women about exposure to Aedes species mosquitos, assess travel history and sexual exposure, and—if indicated—test for Zika virus infection.
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