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Sex Ratios Among Births in British Columbia, 2000-2013

      Abstract

      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.

      Résumé

      Objectif

      Des études antérieures ont rapporté un déséquilibre de la proportion des sexes parmi les naissances vivantes chez certains groupes d'immigrants au Canada. Nous avons mené une étude sur la proportion des sexes en Colombie-Britannique.

      Méthodes

      Ont été comprises dans l'échantillon toutes les mortinaissances et les naissances vivantes chez les résidents de la Colombie-Britannique d'avril 2000 à mars 2013, d'après les données obtenues du Perinatal Data Registry de la Colombie-Britannique. Nous avons déterminé la proportion des sexes pour l'ensemble des naissances ainsi que des interruptions de grossesse qui ont mené à une mortinaissance ou une naissance vivante. Les analyses ont été stratifiées selon le degré d'anomalie congénitale, le lieu de résidence de la mère et la parité.

      Résultats

      L'échantillon à l'étude comprenait 567 225 mortinaissances et naissances vivantes. Dans la Fraser Health Authority, la proportion des sexes pour les naissances sans anomalie congénitale était de 51,3 % de garçons (IC à 95 % : 51,1-51,5); elle était significativement plus élevée que la proportion de 40,7 % de garçons (IC à 95 % : 33,2-48,6) pour les interruptions tardives de grossesse sans anomalies congénitales (P = 0,008). Cependant, pour l'ensemble de la Colombie-Britannique, moins la Fraser Health Authority, les proportions des sexes correspondantes étaient respectivement de 51,1 % (IC à 95 % : 50,9-51,3) et de 51,1 % (IC à 95 % : 45,5-56,7) (P = 0,99). La proportion des sexes pour les naissances de femmes multipares était aussi significativement différente dans la Fraser Health Authority. Seulement une fraction négligeable de la faible proportion de naissances féminines dans la Fraser Health Authority pouvait être expliquée par un déséquilibre de la proportion des sexes parmi les interruptions tardives de grossesse.

      Conclusion

      On constate un déséquilibre de la proportion des sexes pour les mortinaissances et les naissances vivantes chez les résidents de la Fraser Health Authority par rapport à celle qui est observée ailleurs en Colombie-Britannique. Ce déséquilibre est probablement dû à un écart entre les sexes dans les interruptions précoces de grossesse.

      Key Words

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