BACKGROUND AND OBJECTIVES:Perinatal outcomes have improved in developed countries but remain poor for disadvantaged populations. We examined whether an unconditional income supplement to low-income pregnant women was associated with improved birth outcomes.METHODS:This study included all mother–newborn pairs (2003–2010) in Manitoba, Canada, where the mother received prenatal social assistance, the infant was born in the hospital, and the pair had a risk screen (N = 14 591). Low-income women who received the income supplement (Healthy Baby Prenatal Benefit [HBPB], n = 10 738) were compared with low-income women who did not receive HBPB (n = 3853) on the following factors: low birth weight, preterm, small and large for gestational age, Apgar score, breastfeeding initiation, neonatal readmission, and newborn hospital length of stay (LOS). Covariates from risk screens were used to develop propensity scores and to balance differences between groups in regression models; γ sensitivity analyses were conducted to assess sensitivity to unmeasured confounding. Population-attributable and preventable fractions were calculated.RESULTS:HBPB was associated with reductions in low birth weight (aRR, 0.71 [95% CI, 0.63–0.81]), preterm births (aRR, 0.76 [95% CI, 0.69–0.84]) and small for gestational age births (aRR, 0.90 [95% CI, 0.81–0.99]) and increases in breastfeeding (aRR, 1.06 [95% CI, 1.03–1.09]) and large for gestational age births (aRR, 1.13 [95% CI, 1.05–1.23]). For vaginal births, HBPB was associated with shortened LOS (weighted mean, 2.86; P < .0001). Results for breastfeeding, low birth weight, preterm birth, and LOS were robust to unmeasured confounding. Reductions of 21% (95% CI, 13.6–28.3) for low birth weight births and 17.5% (95% CI, 11.2–23.8) for preterm births were associated with HBPB.CONCLUSIONS:Receipt of an unconditional prenatal income supplement was associated with positive outcomes. Placing conditions on income supplements may not be necessary to promote prenatal and perinatal health.