Abstract
AbstractSTUDY QUESTIONAre the decreasing multiple birth rates after ART associated with a simultaneous drop in the incidence of cerebral palsy (CP) in ART children over time?SUMMARY ANSWERThe relative odds of CP in ART children have declined in the Nordic countries over the past two decades concurrently with declining multiple birth rates.WHAT IS KNOWN ALREADYIn the Nordic countries, the rate of twin pregnancies after ART has decreased from 30% in the early 1990s to 4–13% in 2014, following the implementation of elective single embryo transfer (SET). Consequently, preterm birth rates have declined substantially in ART pregnancies. However, whether the risk of CP, a known consequence of preterm birth, has decreased correspondingly is still unknown.STUDY DESIGN, SIZE, DURATIONRetrospective register-based cohort study based on data on all singletons, twins, and higher-order multiples born in Denmark (birth year 1994–2010), Finland (1990–2010), and Sweden (1990–2014), corresponding to 111 844 ART children and 4 679 351 spontaneously conceived children.PARTICIPANTS/MATERIAL, SETTING, METHODSData were obtained from a large Nordic cohort of children born after ART and spontaneous conception initiated by the Committee of Nordic ART and Safety—CoNARTaS. The CoNARTaS cohort was established by cross-linking national register data using the unique personal identification number, allocated to every citizen in the Nordic countries. Data from the National Medical Birth Registers, where info