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.


CONCLUSIONS
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.


METHODS
II-2
Luo
Zhong-Cheng
ZC
Department of Epidemiology and Biostatistics, McGill University, Montreal, Quebec, Canada.
Wilkins
Russell
R
Kramer
Michael S
MS
D001724:Birth Weight; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007086:Illegitimacy; D007231:Infant, Newborn; D008137:Longitudinal Studies; D017533:Marital Status; D008393:Marriage / Q000639:trends; D011247:Pregnancy; D011256:Pregnancy Outcome / Q000453:epidemiology*; D011792:Quebec / Q000453:epidemiology; D012747:Sexual Partners; D015406:Single Parent; D012959:Socioeconomic Factors