Birth order may carry unexpected neurological consequences for preterm twins, challenging assumptions about identical early development in multiples. This finding could reshape neonatal care protocols and parental counseling for high-risk pregnancies involving twins born before 37 weeks gestation.
Chinese researchers tracked 225 twin pairs through their first months of life, documenting neurological development using cranial ultrasounds, brain wave monitoring, and motor assessments. Second-born twins consistently demonstrated elevated rates of neurological complications compared to their first-born siblings, despite sharing identical genetic material in monochorionic cases and nearly identical intrauterine environments. The pattern held across different gestational ages at birth and delivery methods, suggesting birth order itself - rather than pregnancy complications or delivery trauma - drives the disparity.
This research illuminates a previously under-recognized aspect of twin biology that extends beyond the well-documented twin-to-twin transfusion syndrome. The mechanism likely involves positioning within the uterus, with second-born twins potentially experiencing prolonged compression, altered blood flow patterns, or different stress hormone exposure during labor. The findings align with emerging evidence that even brief differences in birth timing can trigger cascading neurological effects in vulnerable preterm brains. However, the study's observational design cannot establish causation, and the relatively short follow-up period leaves questions about long-term developmental trajectories. For neonatal intensive care units, these results suggest birth order should join gestational age and birth weight as key risk stratification factors, potentially warranting enhanced neurological monitoring for second-born preterm twins during their critical early weeks.