Trends in neural tube defects in Scotland 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 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, maternal area-level deprivation quintile.
Main outcome measures: 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 2000-2021, there were 1,178 babies with a recorded NTD (436 anencephaly, 577 spina bifida) and 1,203,491 total births. Total birth prevalence of NTDs was 9.8 [95% CI 9.2, 10.4] per 10,000 total births. Prevalence was lower among babies to mothers aged 30-39 years (compared to younger or older) and those from less (compared to more) deprived areas. There was no evidence of change over the study period in 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). The prevalence of anencephaly showed no change 2000-2012, then increased 2013-2021 (PRR 1.12 [95% CI 1.06, 1.19] p<0.001).
Conclusions: 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.