RESUMO
OBJECTIVE: To evaluate the impact of maternal age and use of fertility drugs on multiple birth prevalence from 1970 to 1995 in the Netherlands. STUDY DESIGN: A population-based survey was carried out in which data were collected from the Centraal Bureau voor Statistiek, the Institute of Medical Statistics and from all clinics for in vitro fertilization. RESULTS: In the last two decades, the prevalence of multiple births, especially of twin and triplet births, has increased significantly. Three possible explanations for this phenomenon are: (1) introduction of assisted reproductive techniques in combination with fertility drugs; (2) increasing maternal age; and (3) decreasing fecundity with increasing maternal age, resulting in more fertility treatments. A surplus of 1,366 twins was born in 1995 as compared to 1975. The expected excess of twins was 1,368, of which 104 (7.6%) were a result of the increase in total births in 1995, 583 (42.6%) were due to maternal age > 29 years, and, respectively, 330 (24.1%) and 351 (25.7%) twins were due to in vitro fertilization treatment and intrauterine insemination. CONCLUSION: The delay in achieving pregnancy and the use of fertility-promoting therapies profoundly affect the prevalence of multiple pregnancies in a given country. The general population should be informed of this risk.
