Multiple births in an era of assisted reproduction and delayed motherhood: Evidence from Czechia and an international comparison

This article examines recent international trends regarding multiple births, with a specific focus on Czechia. It stresses the role of assisted reproductive technology (ART) along with the fertility postponement process. Employing internationally harmonised datasets and detailed Czech data on deliveries and live births, we firstly provide a comparative overview of long-term trends concerning twinning/multiple birth rates prior to and following the widespread use of ART. Based on anonymised individual-level data for Czechia, we explore the role of ART and the maternal age in determining the proportion of multiple births and the structure of newborns. Particular attention is devoted to differences according to the maternal age and the mode of conception (with and without the use of ART). The results revealed the substantial international heterogeneity of twinning rates as driven primarily by differences in national ART practices rather than the overall volume of ART treatment. Czechia represents the most common pattern, i.e. a rapid increase in the twinning rate from less than 10 twin deliveries per 1,000 deliveries in the early 1990s to more than 21 twin deliveries per 1,000 in 2010, followed by a rapid decline. Regulatory changes in Czechia that have promoted single embryo transfers since 2012 have led to a marked decline in the incidence of multiple births. However, women aged 35 and older accounted for a significant share of multiple live births conceived through ART; 18% of all multiples born to women aged 35–39, and 36% of those born to women aged 40 and over, were conceived via ART in 2020.