Disparities in pregnancy outcomes according to marital and cohabitation status.

OBJECTIVE

To assess the risks and trends of adverse pregnancy outcomes among mothers in common-law unions versus traditional marriage relationships.

METHODS

We conducted a birth cohort-based study of all 720,586 births registered in Quebec for the years 1990 to 1997.

RESULTS

The proportion of births to common-law mothers more than doubled from 20% in 1990 to 44% in 1997. Preterm birth, low birth weight, small for gestational age, and neonatal and postneonatal mortality rates increased progressively from mothers legally married, to common-law unions, to lone mothers with father information, to lone mothers without father information on birth registrations. Adjusted odd ratios with 95% confidence intervals (CIs) for common-law versus legally married mothers were 1.14 (95% CI 1.11, 1.17) for preterm birth, 1.21 (95% CI 1.18, 1.25) for low birth weight, 1.18 (95% CI 1.16, 1.20) for small for gestational age, 1.07 (95% 0.97, 1.19) for neonatal death, and 1.23 (95% CI 1.04, 1.44) for postneonatal death after controlled for observed individual- and community-level characteristics. The crude and adjusted odds ratios were virtually unchanged over time.

CONCLUSION

Pregnancy outcomes are worse among mothers in common-law unions versus traditional marriage relationships but better than among mothers living alone. Modest disparities in pregnancy outcomes in common-law versus traditional marriage relationships have persisted despite the striking rise in common-law unions.

LEVEL OF EVIDENCE: II-2