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RESEARCH PRODUCT

Prevalence of microcephaly in Europe: population based study.

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Objectives: Microcephaly is a congenital anomaly where the baby’s head is smaller than expected when compared with babies of the same sex, age and ethnicity. Many of these babies will have underdeveloped brains. This study aimed to provide contemporary estimates of the prevalence of microcephaly in Europe, determine if the diagnosis of microcephaly is consistent across Europe and to evaluate whether changes in prevalence would be detected using the current European surveillance performed by EUROCAT (the European Surveillance of Congenital Anomalies). Design: A questionnaire and a population-based, observational study Setting: 24 EUROCAT registries covering 570,000 births annually in 15 countries. Participants: 2443 cases of microcephaly not associated with a genetic condition, among live births, fetal deaths from 20 weeks gestational age and terminations of pregnancy for fetal anomaly at any gestation. Main Outcome Measures: Prevalence of microcephaly (1st Jan 2003- 31st Dec 2012) analysed using random effects Poisson regression models to account for heterogeneity across registries. Results: Sixteen registries responded to the questionnaire of whom 44% (7/16) used the EUROCAT definition of microcephaly (a reduction in the size of the brain with a skull circumference more than 3 standard deviations (SD) below the mean for sex, age and ethnic origin), 19% (3/16) used a 2 SD cut-off, 31% (5/16) were reliant on the criteria used by individual clinicians and one registry changed criteria between 2003 and 2012. Prevalence of microcephaly in Europe was 1.53 (95% CI : 1.16-1.96) per 10,000 births with registries varying from 0.4 (95% CI : 0.2-0.7) to 4.3 (95% CI : 3.8-4.8) per 10,000 (Chi-squared =338 with 23 degrees of freedom, I2 = 93%). Registries with the 3 SD cut-off reported a prevalence of 1.74 per 10,000 (95% CI: 0.86-2.93) compared with those with the less stringent 2 SD cut-off of 1.21 per 10,000 (95% CI: 0.21-2.93). The prevalence of microcephaly would need to increase in 1 year by over 35% in Europe or by over 300% in a single registry to reach statistical significance (p<0.01). Conclusions: EUROCAT could detect increases in the prevalence of microcephaly due to the Zika virus of a similar magnitude to those observed in Brazil. However, due to the rarity of microcephaly and discrepant diagnostic criteria, the smaller increases expected in Europe would be unlikely to be detected. Clear diagnostic criteria for microcephaly must be adopted across Europe.