Objective. To study stillbirths and neonatal mortality in the postterm period.
Design. Register study of information obtained from the Swedish Medical Birth Registry (MBR), National Board of Health and Welfare, Stockholm.
Methods. Singleton pregnancies with deliveries occurring between 1982 and 1991 were selected involving 914,702 women (of whom 76,761 had a postterm pregnancy continuing beyond the 42nd week of amenorrhea). All 2,043 records of dead infants were scrutinized before analysis of neonatal deaths. Stratification was made for year of birth, maternal age, and parity.
Results. Generally, the rates of stillbirths and neonatal deaths were low. The stillbirth rate was highest for primiparas at 38 completed weeks (2.72‰), lowest at 40 weeks (1.23‰), then increasing to 2.26% in the postterm period. The difference v. multiparas was significant from 41 weeks onwards. Neonatal mortality was increased at 41 completed weeks for primiparas, but for multiparas it changed significantly first in the postterm period. The OR for a primipara to have an intrauterine death increased from 1.50 at 41 weeks (1.0 at 40 weeks) to 1.79 at 42 weeks and beyond. The OR for multiparas showed no sign of increase as gestation progressed.
Conclusions. The results of this study indicate an increased risk of stillbirth with gestational age for primiparas but not for multiparas. The neonatal death rate was increased for both primiparas and multiparas (after 42 completed weeks).