Population-based study of the incidence of congenital hip dysplasia in preterm infants from the Survey of Neonates in Pomerania (SNiP)

Background: Some etiological factors involved in developmental dysplasia of the hip (DDH) occur in the last trimester of pregnancy, which could result in a decreased incidence of DDH in preterm infants. The aim of this study was to compare the incidence of DDH between preterm and term infants. Methods: Ultrasound of the hip joint was performed in 2,534 term infants and 376 preterm infants within the population-based Survey of Neonates in Pomerania (SNiP) study. Results: A total of 42 (1.66%) term infants had DDH (Graf type II c, 0.8%; type D, 0.3% left and 0.4% right; type III a, 0.2% left). Eighteen infants had bilateral findings. Hip dysplasia occurred more frequently in female neonates (32/1,182 vs. 10/1,302, p < 0.023; 95% CI 0.012-0.022,.2 test). A familial disposition for DDH was found in 169 (6.7%) term infants and 181 (7.1%) infants in the overall population. In preterm infants, dysplasia of the hip was found in only three late preterm infants with gestational age between 36 and 37 weeks (n = 97) and not in preterm infants <36 weeks gestational age (n = 279). Regression analysis revealed a narrowly significant association between gestational week of birth and DDH (relative risk = 1.17; 95% confidence interval 0.99-1.37; p = 0.065). Conclusion: Our study suggests that preterm infants < 36 weeks gestational age have a decreased risk of DDH.