Total and live birth prevalence of singleton pregnancies with Down's syndrome in Scotland between 2000 and 2021: a population-based study

Background: Down's syndrome (DS) is the most common chromosomal congenital condition diagnosed in pregnancy. Antenatal screening for DS is available in Scotland, and in September 2020, non-invasive prenatal testing (NIPT) was added to the screening pathway. This study aimed to examine trends in total birth (TB) and live birth (LB) prevalence of DS (2000-2021) in Scotland and associations with maternal and infant socio-demographic factors. Methods: A retrospective, observational, population-based study using the Scottish Linked Congenital Conditions Dataset (SLiCCD). Poisson and generalised Poisson regression analyses were used to model TB and LB prevalences of DS. Associations with year, maternal age, Scottish Index of Multiple Deprivation, health board of residence, and infant sex (live births only) were assessed. Prevalence rate ratios (PRR), 95% confidence intervals (CIs) and p values were reported. Findings: There were 2098 singleton pregnancies and 1135 live births with DS (2000-2021), with a TB prevalence of 17.4 (95% CI 16.7, 18.2) per 10,000 TBs, and LB prevalence of 9.5 (95% CI 8.9, 10.0) per 10,000 LBs. There was evidence of a non-linear time trend in TB prevalence, increasing between 2013 and 2015 [PRR: 1.13 (95% CI 1.07, 1.19); p < 0.001] and decreasing between 2016 and 2021 [PRR: 0.95 (95% CI 0.92, 0.98); p = 0.002]. No time trend was observed for LB prevalence. Maternal age and health board of residence were associated with TB and LB prevalence of DS. Interpretation: Our population-based insights into TB and LB prevalence of DS in Scotland are important in establishing baseline trends to investigate the impact of NIPT. This enables up-to-date counselling for those undergoing DS screening, and appropriate planning of healthcare services. Funding: ES received Medical Research Scotland PhD Studentship funding (grant no. PHD-50200-2020).