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
Authors: Kirolos Amir , Vieira Rute , Calvert Clara , Griffiths Emily , Wood Rachael 
Published: November 2024

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.

What is already known on this topic

- Recommendations for voluntary fortification of some foods, and for pre-conception daily supplements of folic acid, have been in place since the 1980s and 1990s respectively to support prevention of neural tube defects (NTDs).

- Most women do not take folic acid supplements before conception, and uptake is particularly low in younger mothers and those from poorer socioeconomic backgrounds.

- Legislation to mandate the fortification of non-wholemeal wheat flour with folic acid was introduced in November 2024. This provides an opportunity to improve the equitable prevention of NTDs.

What this study adds

- There is no evidence that the total birth prevalence of NTDs in Scotland changed 2000-2021. Prevalence was lowest among mothers in the 30-39 year age group, and those from less deprived areas.

- There is no evidence that the total birth prevalence of spina bifida in Scotland changed 2000-2021, however the prevalence of anencephaly increased 2013-2021, likely reflecting increasing early antenatal detection of this condition through ultrasound scans.

How this study might affect research, practice, or policy

- This study provides baseline information for the period before the introduction of mandatory fortification. It will be used to support the evaluation of mandatory fortification, and hence guide future policy development.