The social gradient in infant health from a couple-level perspective: Revisiting the heterogamy penalty hypothesis

This study examines how couples’ educational configurations shape infant health. Although the positive relationship between maternal education and infant health is well-established, less is known about the joint and relative contributions of both parents’ education. Yet, the heterogamy penalty hypothesis suggests that couples with dissimilar educational status face greater stressors than their homogamous counterparts, potentially resulting in unequal gestational outcomes. We revisit this assumption using Austrian register data (N = 455,191 singleton births to 355,119 different-sex couples) and by applying Diagonal Reference Models to disentangle the independent association of educational dissimilarity with infant health, net of parents’ educational levels. Results show a large couple-level educational gradient: infants born to higher-educated homogamous parents face markedly lower risks of preterm birth, low birth weight, and fetal growth restriction. Additionally, we find that maternal and paternal education contribute relatively equally to infant health. However, we find no evidence that educational dissimilarity within couples, whether hypogamy or hypergamy, substantially contributes to inequalities in birth outcomes once absolute parental education is taken into account. Overall, our findings underscore the primacy of joint parental educational resources in determining early-life health outcomes.