Multiple birth prevalence in The Netherlands. Impact of maternal age and 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 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.