Sex Ratios Among Births in British Columbia, 2000-2013.

OBJECTIVE: Previous studies have reported distorted sex ratios among live births within specific immigrant groups in Canada. We carried out an investigation into sex ratios in British Columbia.

METHODS: All stillbirths and live births to residents of British Columbia from April 2000 to March 2013 were included in the study, with data obtained from the British Columbia Perinatal Data Registry. We examined sex ratios among births and among pregnancy terminations that resulted in a stillbirth or live birth. Analyses were stratified by congenital anomaly status, maternal residence, and parity.

RESULTS: The study population included 567 225 stillbirths and live births. In the Fraser Health Authority, the sex ratio among births without congenital anomalies was 51.3% males (95% CI 51.1 to 51.5); this was significantly higher than the sex ratio of 40.7% males (95% CI 33.2 to 48.6) among late pregnancy terminations without congenital anomalies (P = 0.008). However, in British Columbia, excluding the Fraser Health Authority, the same sex ratios were 51.1% (95% CI 50.9 to 51.3) and 51.1% (95% CI 45.5 to 56.7), respectively (P = 0.99). Sex ratios among births to multiparous women were also significantly different in the Fraser Health Authority. Only a negligible fraction of the shortfall in female births in the Fraser Health Authority could be explained by sex ratio distortions among late pregnancy terminations.

CONCLUSION: Sex ratios among stillbirths and live births to residents of the Fraser Health Authority are distorted relative to those observed elsewhere in British Columbia. This is likely due to sex differences in early pregnancy terminations.