MULTIPLE BIRTH PREVALENCE IN THE NETHERLANDS - IMPACT OF MATERNAL AGEAND ASSISTED REPRODUCTIVE TECHNIQUES

OBJECTIVE: To evaluate the impact of maternal age and use of fertility drugs on multiple birth prevalence from 1970 to 1995 in the Netherlan ds. STUDY DESIGN: A population-based survey was carried out in which d ata were collected from the Central Bureau voor Statistics, the Instit ute of Medical Statistics and from all clinics for in vitro fertilizat ion. RESULTS: In the last two decades, the prevalence of multiple birt hs, especially of twin and triplet births, has increased significantly . Three possible explanations for this phenomenon are: (1) introductio n of assisted reproductive techniques in combination with fertility dr ugs; (2) increasing maternal age; and (3) decreasing fecundity with in creasing maternal age, resulting in more fertility treatments. A surpl us of 1,366 twins was born in 1995 as compared to 1975. The expected e xcess of twins was 1,368, of which 104 (7.6%) were a result of the inc rease 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 du e to in vitro fertilization treatment and intrauterine in semination. CONCLUSION: The delay in achieving pregnancy and the use of fertility- promoting therapies profoundly affect the prevalence of multiple pregn ancies in a given country. The general population should be informed o f this risk.