This study examines trends in multiple pregnancies in Denmark from 1980 to 1994, focusing on changes not explained by maternal age and parity patterns. Using national records, the researchers analyzed 497,979 Danish women and 803,019 pregnancies. The results show a 1.7-fold increase in multiple pregnancies during the study period, primarily among primiparous women aged 30 years and older. The adjusted twinning rate increased 2.7-fold, and the triplet rate increased 9.1-fold. The proportion of multiple births among infant deaths among primiparous women aged 30 years and older increased from 11.5% to 26.9%. Despite this, total infant mortality did not increase due to a significant decrease in infant mortality among singletons. The study concludes that a small group of women with fertility treatments has significantly impacted national rates of multiple pregnancies and infant mortality, suggesting that resources associated with these treatments are substantial.This study examines trends in multiple pregnancies in Denmark from 1980 to 1994, focusing on changes not explained by maternal age and parity patterns. Using national records, the researchers analyzed 497,979 Danish women and 803,019 pregnancies. The results show a 1.7-fold increase in multiple pregnancies during the study period, primarily among primiparous women aged 30 years and older. The adjusted twinning rate increased 2.7-fold, and the triplet rate increased 9.1-fold. The proportion of multiple births among infant deaths among primiparous women aged 30 years and older increased from 11.5% to 26.9%. Despite this, total infant mortality did not increase due to a significant decrease in infant mortality among singletons. The study concludes that a small group of women with fertility treatments has significantly impacted national rates of multiple pregnancies and infant mortality, suggesting that resources associated with these treatments are substantial.