Background Neural tube defects (NTD) are often lethal brain and spinal cord malformations with serious lifelong morbidity among survivors. Folates consumed before and during early pregnancy reduce the risk of NTD. Folate insufficiency has been related to isolated-NTD. Since the mid-1990s programs to increase folate consumption have reduced NTD overall, but not among teenagers. The addition of folic acid (synthetic folate) to bread-making flour became mandatory in Australia from September 2009 to increase folate consumption among all women of reproductive age.

This before-an-after study looked for change in NTD prevalence rates.

Methods NTD prevalence rate is number of NTD among births or pregnancy terminations for congenital anomaly relative to the number of total births. Five states and territories provided data for 1014 NTD (ICD9-BPA 740.00–740.29, 741.00–741.99, 742.00–742.09) from births and pregnancy terminations in 2007–2011. Jurisdictional ascertainment methods varied, but were consistent over the study period. Pregnancy populations were defined in time by date of conception and place by maternal residence. NTD prevalence rates among conceptions in the baseline period (October 2006 to December 2008), were compared with those in the standard period (October 2009 to March 2011). Denominators for the same populations were from national birth data. Isolated-NTD (no co-existing causally-unrelated anomaly) and non-isolated NTD were distinguished. NTD relative rates (RR) and relative percentage differences ((1-RR)*100) used the baseline period as reference.

Results The best estimates of NTD prevalence among babies of teenage mothers was 18.6 per 10,000 conceptions in the baseline period that ended as a birth and 7.0 per 10,000 conceptions in the standard period that ended as a birth, representing a statistically significant fall of 62.6% (95% CI: 9.1, 86.7). The relative percentage differences were 24.6%, 17.2% and 14.4% respectively babies of mothers aged 20–24, 25–29, and 30–34 years. These falls were statistically non-significant but reduced progressively with increasing age. Among babies of mothers 35 years or older NTD prevalence rates increased 32.6% (95% CI: −9.7, 94.6). The strong downward trend in isolated-NTD prevalence rates with maternal age in the baseline period disappeared in the standard period.

Conclusion This is the first demonstration of a substantial fall in NTD prevalence among babies of teenagers in Australia. Findings among older mothers suggest folate sufficiency and the need to look for causes of NTD. Longer time series and information about other known risk factors, particularly obesity and diabetes, are needed to confirm these findings.