Accuracy of ultrasound scanning relative to reference tests for prenatal diagnosis of microcephaly in the context of Zika virus infection: a systematic review of diagnostic test accuracy

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Evidence suggests that prenatal ultrasound appears more accurate in detecting the absence of microcephaly than its presence.

In 2015, a 20-fold increase in neonatal microcephaly was observed in association with Zika virus infection in pregnant women in Latin America. There is no international consensus on the fetal biometric parameter or the threshold to confidently diagnose microcephaly in utero by ultrasound. This systematic review assessed the accuracy of ultrasound measurements of fetal biometric parameters for prenatal diagnosis of microcephaly. Nine studies were included. No study including Zika virus-infected pregnant women was identified. Pooled estimates from two studies showed that at 3, 4 and 5 standard deviations below the mean, sensitivities were between 94-58% and specificities between 16-97% for head circumference, occipito-frontal diameter and biparietal diameter. Extrapolated positive predictive values for Zika virus-infected pregnancies at same standard deviations were between 1-16% and negative predictive values were over 99% for the same parameters. Five out of seven studies with descriptive data reported high rates of false positives when ultrasound is applied for prenatal diagnosis of microcephaly. All studies had some concern for risk of bias.

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