Sex Assigned at Birth and Early Childhood Outcomes Among Children Born Preterm.

IMPORTANCE: Preterm birth is a leading cause of childhood morbidity. Although survival has improved, sex-specific differences in postnatal health outcomes remain insufficiently studied. Understanding how sex assigned at birth influences early health trajectories is essential to guide counseling, follow-up care, and public health planning. OBJECTIVE: To examine sex-specific differences in health care utilization, morbidities, and medication use among children born preterm. DESIGN, SETTING, AND PARTICIPANTS: This population-based cohort study used linked administrative health databases in British Columbia, Canada. Participants included children born at a gestational age (GA) of 22 to 44 weeks, from April 1, 2004, to December 31, 2014, followed up from 6 months to 5 years of age. Follow-up was completed December 31, 2019. Children were excluded if they had missing GA, sex, or birth weight, incomplete data linkage, or loss of registration in the provincial databases. Data were analyzed June 3, 2026. EXPOSURES: GA categories (22-27, 28-33, 34-36, and ≥37 weeks) and sex assigned at birth. MAIN OUTCOMES AND MEASURES: Health service utilization (hospitalizations and physician visits), morbidities (identified using International Classification of Diseases, Ninth Revision, and International Statistical Classification of Diseases, Tenth Revision, Canada), and dispensed medications between 6 months and 5 years of age. Rate ratios (RRs) and 95% CIs were estimated using Poisson regression. RESULTS: Among the 448 815 children included in the analysis, 42 080 (9.4%) were born preterm and 230 351 (51.3%) were male. Compared with female infants, male infants born at 22 to 27 weeks' gestation were more likely to be small for GA (30 of 547 [5.5%] vs 48 of 597 [8.0%]) and less likely to have a 5-minute Apgar score above 7 (237 of 544 [43.6%] vs 212 of 590 [35.9%]). Across all GA categories, males had higher rates of hospitalization and use of physician services than females; the magnitude of association did not vary by GA. Male children had greater prevalence of asthma, bronchiolitis, and growth and developmental disorders. Females had consistently lower rates of oral corticosteroid prescription across GA groups (RRs, 0.74 [95% CI, 0.71-0.76] to 0.80 [95% CI, 0.75-0.85]) than male children. Rates of antibiotic and bronchodilator prescriptions were higher in males, except for antibiotic prescriptions among those born at 22 to 27 weeks' gestation. CONCLUSIONS AND RELEVANCE: In this cohort study examining sex-specific differences in early childhood health outcomes, male children experienced higher rates of health care utilization and prevalence of several common morbidities and medication use. These findings highlighted the need for sex-informed approaches in pediatric follow-up care and public health strategies.