The effect of perinatal screening in Norway on the magnitude of noninherited risk factors for congenital dislocation of the hip.

Several investigators have noted an increase in the rate of congenital dislocation of the hip shortly after the initiation of neonatal screening procedures. This increase has been attributed to the detection of temporarily unstable hips which require no corrective treatment. To test whether neonatal screening had low specificity, the authors obtained data on 17,145 offspring of 7,896 twins from the Norwegian Twin Panel. Information from maternal reproduction history questionnaires was available on the presence or absence of congenital dislocation of the hip, type of obstetric delivery, and parity. The reported prevalence of the disorder did indeed begin to rise sharply during the late 1950s, at which time neonatal screening started in Norway. Infants were then grouped by year of birth (born before or after 1960), and odds ratios were calculated for breech delivery and early (first or second) parity. For the pre-screening group, the odds ratio of congenital dislocation of the hip was 7.7 among children delivered by breech presentation and 2.6 among those of early parity. These values are similar to those found in other studies. In the post-screening group, the odds ratios for breech delivery and early parity were 1.5 and 1.2, respectively. Breech delivery and early parity have been consistent risk factors for congenital dislocation of the hip. Their diminished influence in the post-screening group, as well as sharply increased rates of the disorder, suggests that in Norway neonatal screening programs may have had low specificity in detecting cases that required treatment.