THE IMPACT OF INTRAUTERINE FACTORS ON NEONATAL HIP INSTABILITY - AN ANALYSIS OF 1,059,479 CHILDREN IN NORWAY

The records of the Medical Birth Registry of Norway from 1970 through 1988 contain information on maternal health, course of delivery and he alth of 1,059,479 newborns. The overall prevalence at birth of neonata l hip instability (NHI) was 0.9 percent: 0.6 percent in boys and 1.4 p ercent in girls. In breech presentation, the rate was 4.4 percent. In vaginally delivered children, the rate was only marginally higher comp ared to those delivered by cesarean section. In children with a birthw eight less than 2,500 g, the rate was 0.3 percent. In vertex presentat ion, the duration of pregnancy had no influence in boys whilst, in bre ech presentation, the prevalence increased up to the 39th week of gest ation. In girls, the NHI rate increased with the duration of gestation , particularly in breech presentation. In first-born children, these p atterns were even more obvious. The data are consistent with a hypothe sis that intra-uterine mechanical factors, in combination with hormona l factors, are of importance rather than the actual trauma of vaginal delivery.