Impact of National Screening Programs on Down syndrome prevalence and outcomes

Over the past five decades, antenatal screening programs have evolved significantly, primarily through advancements in ultrasound technology and the shift from invasive to non-invasive prenatal testing methods. This study aimed to evaluate the impact of these developments in prenatal screening for Down syndrome (DS) on the prevalence of live and stillbirths, as well as terminations of pregnancy (TOP) with DS.

This population-based registry study included all pregnancies in Norway from 1967 to 2021, with data on TOPs available from 1999. Information on DS pregnancies was obtained from the Medical Birth Registry of Norway. Logistic regression models were applied to evaluate time trends and maternal characteristics associated with TOP.

Among 3 231 159 pregnancies, 4764 (0.147%) were affected by DS. The prevalence of DS pregnancies increased from 0.165% in 1999 to 0.251% in 2021. During this period, the proportion of TOP rose from 20% to 55%, while prenatal detection rates improved from 18% to 70%. Despite increased detection, the proportion of TOP following prenatal diagnosis remained stable at approximately 80%. The prevalence of live births with DS remained stable at approximately 0.106%, while the prevalence of stillbirths was around 0.008%. Maternal age, parity, country of birth, and region of residence were associated with TOP decisions. Mean gestational age at termination decreased from 17.5 to 15.7 weeks.

Over recent decades, prenatal detection and termination of DS pregnancies have increased. However, the proportion of women continuing pregnancies after a prenatal diagnosis and the prevalence of live- and stillbirths with DS have remained stable.