Background: Marked changes have occurred in in vitro fertilization (IVF) methodology during the past 25 years but also in characteristics of couples undergoing treatment.
Methods: This study was based on 27 386 women undergoing IVF treatment from 1982 to 2006 and giving birth to 31 850 infants. Outcomes of deliveries were studied using Swedish health registers. Comparisons were made with all deliveries in the population (n = 2 603 601). Adjusted odds ratios were calculated when important changes in background rates had occurred.
Results: There was a substantial increase in the use of intracytoplasmatic sperm injection (ICSI) and the transfer of cryopreserved embryos. Among all ICSI cases, the proportion using epididymal or testicular sperm varied between 5 and 10%. Maternal characteristics changed during the observation period but the median age remained relatively constant in spite of the increasing maternal age in the population. There was a decline in the rate of some maternal pregnancy diagnoses (notably pre-eclampsia, premature rupture of membranes) and some neonatal diagnoses (notably preterm births, low birthweight, cerebral hemorrhage, respiratory diagnoses, use of continuous positive airway pressure and mechanical ventilation, sepsis/pneumonia). Up till 1992, the twinning rate increased to a maximum of about 30% and then declined to 5% towards the end of the period whereas higher order multiples nearly disappeared. The total rate of infants with congenital malformations changed only little.
Conclusions: The decrease in unwanted outcomes can, to a large extent, be explained by the reduced rate of multiple births but was seen also among singletons. Other explanations can be sought in changes in the characteristics of patients undergoing IVF.