Interpregnancy Interval and Congenital Anomalies: A Record-Linkage Study Using the Manitoba Population Research Data Repository.

Objective: Congenital anomalies are a serious public health issue, and relatively few modifiable risk factors have been identified. Our objective was to investigate one such potential risk factor, the interpregnancy interval (IPI).

Methods: We conducted a secondary analysis of data housed at the Manitoba Centre for Health Policy. In-hospital live births and stillbirths of at least 20 weeks' gestation were identified, and consecutive births to the same mother were grouped into sibling pairs to calculate the IPI for the younger siblings of each pair. Logistic regression models were fit to examine the association between the IPI and any congenital anomaly, as well as CNS and chromosomal anomalies, while controlling for potentially confounding sociodemographic and clinical factors.

Results: Among 172 909 live births and stillbirths, the IPI was not significantly associated with congenital anomalies overall or with chromosomal anomalies. Short IPIs were associated with significantly increased odds of CNS anomalies relative to IPIs of 18-23 months (adjusted OR [aOR] for IPIs <6 months 2.15; 95% CI 1.48-3.12), whereas the aOR for IPIs ≥60 months was elevated but not statistically significant (aOR 1.50; 95% CI 0.96-2.34). In a sensitivity analysis in which the cohort was restricted to births from 2003 onwards (which yielded more complete data on health-related behaviours), the observed effect for IPIs shorter than 6 months and CNS anomalies was attenuated and no longer significant, but it remained elevated (aOR 1.65; 95% CI 0.85-3.24).

Conclusion: The findings for CNS anomalies warrant further investigation.