[Pregnancy, births and infants after in-vitro-fertilization in Norway, 1988-1991].

We studied 1,165 pregnancies after in vitro fertilization in six public hospitals in Norway in the years 1988-91. The annual number of pregnancies increased from 158 in 1988 to 365 in 1991. The mean number of replaced embryos was reduced from 3.7 to 2.7. The rate of multiple births was not significantly altered in the same period, 24.3% were twin births and 5.7% triplet births. 19.3% of the pregnancies ended in abortion and 8.4% were ectopic. 782 births were registered in the Medical Birth Registry of Norway and compared with all other births during the period. Gestational hypertension, bleeding and preterm birth were observed more often in pregnancies after in vitro fertilization. The proportion of infants with very low birth weight (> 1,500 g) after in vitro fertilization was 9.7%, and nearly 50% of these were triplets. The relative risk of stillbirth and death during the first year of life, adjusted for maternal age and birth order, was 3.1 (95% CI 2.4-4.0) and 2.3 (95% CI 1.5-3.5) for singletons alone. The proportion of multiple births should be reduced.