Compared to moderate levels of drinking, both abstinence and heavier drinking in late adolescence/early adulthood predicted greater likelihood of lifetime childlessness and fewer children

Alcohol consumption at age 18-25 and number of children at a 33-year follow-up individual and within-pair analyses of Finnish twins. Richard J. Rose et al. Alcoholism, June 19 2022. https://doi.org/10.1111/acer.14886

Abstract

Background: Do drinking patterns in late adolescence/early adulthood predict lifetime childlessness and number of children? Past research is but tangentially relevant, inconsistent in results, and compromised in design. Genetic and environmental confounds are poorly controlled; covariate effects of smoking and education often ignored; males are understudied; population-based sampling is rare, and long-term prospective studies with genetically informative designs are yet to be reported.

Method: In a 33-year follow-up, we linked drinking patterns of >3,500 Finnish twin pairs, assessed at ages 18-25, to registry data on their eventual number of children. Analyses distinguished associations of early drinking patterns with lifetime childlessness from those predictive of family size. Within-twin pair analyses used fixed-effects regression models to account for shared familial confounds and genetic liabilities. Childlessness was analyzed with Cox proportional hazards models and family size with Poisson regression. Analyses within-pairs and of twins as individuals were made before and after adjustment for smoking and education, and for oral contraceptive use in individual-level analyses of female twins.

Results: Baseline abstinence and heavier drinking significantly predicted lifetime childlessness in individual-level analyses. Few abstinent women used OCs, but they were nonetheless more often eventually childless; adjusting for smoking and education, abstinence-childless associations remained. Excluding childless twins, Poisson models of family size found heavier drinking at 18-25 predictive of fewer children in both men and women. Those associations replicated in within-pair analyses of DZ twins, each level of heavier drinking associated with smaller families. Among MZ twins, associations of drinking with completed family size yielded effects of similar magnitude, reaching significance at highest levels of consumption, ruling out familial confounds.

Conclusions: Compared to moderate levels of drinking, both abstinence and heavier drinking in late adolescence/early adulthood predicted greater likelihood of lifetime childlessness and fewer children. Familial confounds do not fully explain these associations.