Objective We assessed baseline prevalence, risk factors and outcomes of microcephaly in a large population of neonates.
Design Retrospective cohort study.
Setting All hospitals in the province of Quebec, Canada.
Participants 794 microcephalic and 1 944 010 non-microcephalic infants born between 1989 and 2012.
Main outcome measures Baseline prevalence of microcephaly and occurrence of other congenital anomalies. We estimated the association of (1) pregnancy risk factors including TORCH infections (toxoplasmosis, rubella, cytomegalovirus, herpes, other), exposure to teratogens, diabetes and maternal congenital anomalies with risk of microcephaly, and (2) microcephaly with risk of infant mortality and severe morbidity, adjusted for maternal characteristics.
Results The overall prevalence of microcephaly was 4.1 per 10 000, ranging between 3.0 and 5.3 per 10 000 over time. Only 37% of microcephalic infants presented with other congenital anomalies. Maternal infection during pregnancy was the strongest risk factor, with 32 times the risk of microcephaly (prevalence ratio 32.38; 95% CI 22.42 to 46.75) compared with no infection. Exposure to teratogens was the next most important risk factor, with three times greater risk (prevalence ratio 3.10; 95% CI 2.37 to 4.07). Microcephaly was associated with 20 times the risk of infant mortality compared with no microcephaly (prevalence ratio 20.52; 95% CI 15.57 to 27.04) and significantly greater infant morbidity.
Conclusions In Canada, infectious exposure during pregnancy is a strong risk factor for microcephaly, and affected infants are at higher risk of poor birth outcomes. Better monitoring of microcephaly is needed in the event that Zika or other novel viruses affect future risk.
- Congenital Abnormalities
- Risk Factors
- Zika Virus
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Contributors NA, JHP and LA contributed to study conception and design. NA and JHP analysed the data, and CQ and AML helped interpret the results. NA and JHP drafted the work, and all authors revised it critically for important intellectual content. All authors approved the version to be published and agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. NA is the guarantor. All authors, external and internal, had full access to all of the data (including statistical reports and tables) in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.
Funding This study was funded by the Canadian Institutes of Health Research (MOP-130452) and the Fonds de recherche du Québec-Santé (career grants awarded to Auger 25128 and Quach 26873).
Disclaimer The funders did not participate in the study design; in the collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the article for publication. The researchers are independent of the funders.
Competing interests None declared.
Ethics approval We obtained an ethics waiver from the review board of the University of Montreal Hospital Centre. The data were de-identified and the study conformed to requirements for ethical conduct of research on humans in Canada.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement No additional data are available.