Trends in neural tube defects in Scotland in 2000-2021 prior to the introduction of mandatory folic acid fortification of non-wholemeal wheat flour: a population-based study.

Objective: To describe the total birth prevalence of neural tube defects (NTDs) in Scotland in 2000-2021.

Design: National, population-based study.

Setting: Scotland, UK.

Participants: Babies with an NTD and pregnancy outcome of live birth, stillbirth (≥20 weeks' gestation) or termination of pregnancy (any gestation), as recorded in the Scottish Linked Congenital Condition Dataset.

Exposures: Year, maternal age group and maternal area-level deprivation quintile.

Main outcome measures: The main outcome measure was the total birth prevalence of all NTDs and separately anencephaly and spina bifida (per 10 000 total births). The association between exposures and outcomes was investigated using Poisson regression.

Results: In Scotland in 2000-2021, there were 1178 babies with a recorded NTD (436 anencephaly, 577 spina bifida) and 1 203 491 total births. The total birth prevalence of NTDs was 9.8 (95% CI 9.2, 10.4) per 10 000 total births. The prevalence was lower among babies born to mothers aged 30-39 years (compared with younger or older mothers) and those from less (compared with more) deprived areas. There was no evidence of change in the prevalence of NTDs (prevalence rate ratio (PRR) 1.01 (95% CI 0.997, 1.02), p=0.16) or spina bifida (PRR 0.99 (95% CI 0.98, 1.01), p=0.35) over the study period. The prevalence of anencephaly showed no change in 2000-2012, but increased in 2013-2021 (PRR 1.12 (95% CI 1.06, 1.19), p<0.001).

Conclusions: The observed trends in anencephaly likely reflect increasing detection in early pregnancy. Current strategies are failing to equitably reduce NTDs in Scotland. Monitoring of future trends is needed to assess the impact of mandatory folic acid fortification.