Abstract
The risk of perinatal death was studied in relation to the tendency for mothers to carry their fetuses to similar gestational ages and birth weights in successive pregnancies. The data for this study are derived from all 635 140 births in Norway during a 10-year period (1967-76). The findings demonstrate that those babies that were born similar in age and size to their elder siblings ran the lowest risk of perinatal death. For example', the perinatal mortality rate (PMR) for second-birth babies weighing between 2501 and 3000 g is 9.1 per 1 000 births if the first baby weighed 3000 grams or less. But the PMR is 50% higher, 13.3 per 1 000 births, when the first baby weighed between 3001 and 3 500 g. If the first baby weighed more than 3 500 g, then the PMR is 3 1/2 times greater, 32.1 per 1000 births.
In addition to gestational age and birth weight, the Medical Birth Registry of Norway also records measurements of crown-heel length. The length data show that babies at greatest risk for perinatal mortality tend to be relative long and thin rather than symmetrically developed. For example, the PMR for second babies weighing between 2501 and 3000 grams who were disproportionately long (>46 cm) was 4.6 times greater than the PMR for the average length babies of the same birth weight. The investigation of cause-specific mortality rates showed that most categories were increased for the higher risk babies. However, congenital malformation was the principal contributor to deaths of the relatively short babies. Conversely, placenta praevia, abruptio placentae, and complications of the umbilical cord were the principal contributors to the mortality of the relatively long babies. These results suggest that any deviation from the expected growth pattern for a fetus of a multiparoiis mother should raise concern about an increased risk for the remainder of her pregnancy and delivery.