Why do so many small infants develop an inguinal hernia?

Prevalence and incidence of inguinal hernia in a representative sample of low birthweight survivors were determined by tracing children at 3 years of age. Prevalence was examined in relation to perinatal factors recorded in hospital case notes, using a logistic regression model to allow for confounding variables. Of the 1074 two year survivors, 995 (93%) were assessed. Seventeen per cent of 497 boys and 2% of 498 girls had a hernia by 3 years of age, a total cumulative prevalence of 9.2%: it was significantly increased by lower birth weight, male sex, neonatal intravenous feeding, and lack of respiratory disease. Neonatal illnesses were otherwise not associated with herniation, and most infants were well when they presented. Peak incidence was at the expected full term of gestation. Bilateral hernias were increasingly more common than unilateral hernias at lower gestational ages. It is proposed that causes of increased abdominal pressure in healthy neonates are important causes of herniation during a critical period of inguinal development.