Table 3 Risk prediction model

Risk score from a logistic regression model to predict DDH in the first eight weeks postpartum. Risk score = − 5.50 + 1.73female sex + 1.51first degree family history + 4.07hip-related factors + 0.48infant birth weight > 4000 g. All variables are coded as binary (0 or 1 for absence or presence of a risk factor), except for infant birth weight. The value − 5.50 is the intercept, and other numbers are the estimated regression coefficients for the predictors, which indicate their mutually adjusted relative contribution to the outcome risk. The regression coefficients represent the log odds ratio for a change of 1 unit in the corresponding predictor. The predicted risk of DDH = 1/1 + e^−riskscore.

Example 1—A newborn whose older sibling received splinting for DDH has a birth weight of 4100 g. She showed no abnormalities on the newborn physical examination, in particular her hips were stable and showed symmetric range of motion. She has a predicted risk of 14% of developing DDH within the first eight weeks of delivery. Interpretation: if 100 newborns with the same risk factors are followed, one will develop DDH within eight weeks of birth.

Example 2—A newborn girl was examined on the second day post-partum before discharge from the maternity unit. The left hip was restricted in movement, in particular in abduction. It appeared that the leg lengths were different. The child’s predicted DDH risk is 86% within the first eight weeks of delivery. Interpretation: if 100 newborns with the same risk factors are followed, ninety will develop DDH within eight weeks of birth