Pregnancy Complications
Infant- and Family-Centered Developmental Care
Respiratory Infections
Neonatal Eye Health
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Rare Diseases
Preterm birth is a leading cause of childhood illness, and its effects can continue long after an infant leaves the neonatal intensive care unit (NICU). Male sex is a known risk factor for complications around birth, but less is known about how sex shapes health in early childhood. A large population-based study from Canada followed nearly 450,000 children, including more than 42,000 born preterm, from 6 months to 5 years of age. Across all gestational ages, boys were hospitalized and saw doctors more often than girls. They were also more frequently diagnosed with asthma, bronchiolitis, and growth and developmental disorders.
Thanks to advances in neonatal care, more infants born preterm survive today. Still, children born preterm remain vulnerable to a range of short- and long-term health challenges. Boys are already known to face a higher risk of complications after preterm birth, such as longer hospital stays. Yet few large studies have looked at whether these differences continue into early childhood.
To explore this question, researchers used linked health records from British Columbia, Canada, a province with universal health care. They followed 448,815 children from 6 months to 5 years of age. Boys and girls were compared within four gestational age groups, ranging from 22 to 27 weeks up to full term.
The study found that boys had higher rates of hospitalization and physician visits than girls in every gestational age group. For example, 44% of boys born at 22 to 27 weeks were hospitalized at least once during follow-up, compared with 36% of girls. Notably, the size of this difference was similar across all gestational age groups. Boys were also more often diagnosed with asthma, bronchiolitis, and growth and developmental disorders. The gap was especially large for growth and developmental disorders, which girls had at roughly one fifth the rate of boys. Medication use followed a similar pattern, with girls receiving fewer oral corticosteroid prescriptions across all gestational age groups.
Boys were prescribed antibiotics and bronchodilators more often as well, except among children born at 22 to 27 weeks, where no clear difference was found. Urinary tract infections were the main exception to the overall pattern, as girls born at 28 weeks or later were more likely to develop them. Notably, even girls born preterm had lower rates of growth and developmental disorders than boys born at full term. For other conditions, such as pneumonia, preterm birth was linked to more illness regardless of sex.
The authors discuss possible explanations for the differences in sex, including differences in immune responses, lung function, and growth before birth, but note that the exact mechanisms remain unclear.
The authors conclude that sex-informed approaches could strengthen follow-up care, parental counseling, and public health planning for children born preterm. For parents, the findings offer helpful context, as boys born preterm were more often diagnosed with respiratory conditions such as asthma and bronchiolitis. For neonatal nurses and other healthcare professionals, the results support considering a child's sex when planning follow-up and counseling families. However, the findings show associations rather than causes, and because diagnoses came from health insurance records, they may not always reflect confirmed illness.
Paper available at: Sex Assigned at Birth and Early Childhood Outcomes Among Children Born Preterm | JAMA Network Open
Full list of authors: Yip, J.S.K.; Aziz Ali, S.; Shen, Y.; Richter, L.L.; Bone, J.N.; Chan, E.S.; Roberts, A.; Lisonkova, S.; Kieran, E.; Yang, C.; Chan, N.H.Y.; Lam, C.K.L.; Ting, J.Y.
DOI: 10.1001/jamanetworkopen.2026.34073
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