Irish neural tube defect prevalence study, 2018-2022: path to national congenital anomaly register?

The majority of Neural Tube Defects (NTD) – a sub-group of congenital anomaly (CA) which cause significant morbidity and mortality – are preventable by folic acid (FA). Current FA policy, reliant on FA supplemention recommendations, is not working and is driving health inequity. Current CA surveillance in Ireland is fragmented and covers just 23% of the population. This study, requested by the Irish Department of Health to inform a decision regarding legislation for FA flour fortification (FAFF), presented an opportunity to develop a new NTD surveillance approach, utilising national electronic data, which could inform future NTD and CA surveillance in Ireland. This was a population-based cross-sectional study. The primary outcome was the observed prevalence of NTD-pregnancy in Ireland for 2018-2022. Cases were defined as infants/foetuses with NTD diagnosis, live born, stillborn or with termination of pregnancy (TOP) outcome. Multi-source case ascertainment was employed, utilising predominantly national electronic datasets (hospital discharge data, national perinatal data, stillbirth and death certificate data and TOP data). Linkage across datasets was based on predefined matching criteria. A new methodology to measure NTD prevalence nationally was established and tested. The NTD prevalence rate in Ireland from 2018-2022, including extrapolated TOP cases, is 1.39/1,000 births (95% CI: 1.25-1.52/1,000), higher than rates identified in previous Irish NTD studies. Odds of NTD-pregnancy were higher among women of lower compared to higher socio-economic status (OR 1.9, 95% CI 1.1–3.2) Access to necessary data, particularly TOP data, was a key challenge. Findings indicate NTD prevalence remains high in Ireland. Enactment of legislation for mandatory FAFF alongside establishment of a national CA surveillance system is recommended, to ensure ongoing national surveillance of NTDs, evidence-based adjustment of fortification and capacity to conduct a FAFF impact assessment.

Key messages

• Current folic acid (FA) strategy to prevent neural tube defects in Ireland is failing and increasing health inequity. The study findings support legislation for mandatory FA flour fortification.

• A national congenital anomaly register is needed for ongoing surveillance of neural tube defects, evidence-based adjustment of fortification and capacity to conduct a fortification impact assessment.