Seasonal variation in newborn hip dysplasia: Unraveling the impact of weather on hip development.

Background: Babies born in winter have greater incidence of developmental dysplasia of the hip (DDH) and related surgeries. How weather conditions impact hip development and how screening program reacts weather issue remain unknown. This study tests a hypothesis that winter born babies have more newborn acetabular dysplasia and laxity that is responsible of later DDH.

Methods: Retrospective data from newborns who had hip ultrasonography in the first 3 days of life were analyzed. The Graf type IIc, III, IV (shallow acetabulum) and type D (laxity) were classified as abnormal. The association and risks of an abnormal hip were analyzed with gender, gestational age, fetal presentation, parity and external temperature of birth month and the last 3 months before birth using the Pearson chi-square test and logistic regression.

Results: A total of 10962 newborns participated in hip ultrasound exams voluntarily in nurseries from 2016 to 2022. Distribution of babies with Graf type I, IIa, IIc, D, III/IV hips were 88.8%, 10%, 0.5%, 0.6%, and 0.1%, respectively. Female was the most significant factor for congenital shallow acetabulum (3.8x) and hip laxity (4x) compared to male (p < 0.001). Preterm babies had a borderline lower risk of abnormal hips (0.4x, p = 0.05). Winter season is not associated with newborn abnormal hips (p = 0.36, statistical power = 80%), but a positive correlation was noted between external temperature and incidence of abnormal hips (r = 0.62, p = 0.03). Cold weather does not have a direct internal effect in acetabular dysplasia or hip laxity at birth.

Conclusions: Babies who were born in winter were not associated with acetabular dysplasia and hip laxity at birth but had greater risks of late-diagnosed DDH and surgeries. The postnatal effects from weather should be addressed by a public awareness campaign, and hip screening may not be limited on the neonatal stage.

Level of evidence: level III, diagnostic.