Sudden infant death in Copenhagen 1956--1971. III. Perinatal and perimortal factors.

139 cases of the Sudden Infant Death Syndrome (SIDS) among infants born in the Municipality of Copenhagen during the period 1956--1971 were analysed on the basis of data collected from police reports and (for 131 cases) from the infant health visitors' records. In the SIDS group there was a greater male preponderance than among others dying in the same age range. Compared with the living controls, the SIDS mothers had attended less prenatal examinations, more often delivered their babies at home; the SIDS parents were younger, and yet the SIDS infants were less often firstborns. There was no difference with respect to history of abortions, maternal state of health during pregnancy, or events at delivery. The age at death for the SIDS infants is of a distribution similar to that for fatal respiratory infections. Prematures died later than matures, but this difference is not statistically significant. It is concluded that perinatal factors and SIDS are correlated, but owing to changes in predisposing factors and decreasing differences between cases and controls in recent years as well as interdependence of the factors, it seems doubtful whether the incidence of SIDS can be reduced by alleviating the above-mentioned unfavourable factors.