What has happened with neural tube defects and womens’ understanding of folate in Victoria since 1998?

Neural tube defects (NTDs) are an important group of potentially preventable birth defects. Primary prevention interventions at population level have included efforts to increase awareness of the protective effect of adequate folate levels in the periconceptional period, as well as the introduction of folic acid supplements and fortification of basic foods with folic acid. The definitive evidence on the effectiveness of folate in NTD prevention is summarised in a Cochrane review.1 Since 1993, the National Health and Medical Research Council (NHMRC) has recommended that all women of childbearing age should be offered advice about a folate-rich diet and offered folic acid supplementation with 0.5 mg per day in standard-risk pregnancies and 5 mg per day in higher-risk pregnancies (ie, for women with a family history of NTDs).2 In this article, “folate” refers to the naturally occurring dietary form, but also to both folate and the synthetic equivalent, folic acid (used in supplements and to fortify food), when referring to awareness of the role of folate in pregnancy.

The issues around fortification of foods as a strategy to improve periconceptional folate levels have been widely reviewed by Food Standards Australia New Zealand.3 Folate fortification of foods in Australia was implemented in 1997, and remains voluntary pending implementation of new recommendations. Subsequent modest rises in serum or red-cell folate levels in women of child bearing age were reported in women in Victoria (19% increment from pre-1996 to 2000 levels)4 and Perth (increment of 38% from pre-fortification to 2001).5 The recent decision to introduce mandatory fortification of bread flour in Australia and New Zealand aims to approximately double the current mean folic acid dietary intake, with a fortified diet supplying an estimated 200 μg of folic acid per day.3

Given that the protective effect of folic acid supplementation is dose-dependent,6-8 such a modest increase in folate intake will potentially reduce the prevalence of NTD-affected pregnancies and related terminations by 15%.9 Further supplementation will be required to achieve the lower prevalences of NTDs seen in other countries.1 Therefore, public awareness of the role of folate in reducing the likelihood of NTDs remains extremely important. Since voluntary fortification was introduced in 1997, a folate awareness campaign was launched in Victoria in 1999. A trial to assess the level of folate awareness in the target population before this campaign reported a baseline level of awareness of 12%.10 No further folate awareness strategies have been implemented in Victoria since this time.

Our aims in this study were to determine the prevalence of NTDs reported to the Victorian Birth Defects Register (VBDR) and to examine risk factors for the period 1998–2006, and then to compare these results with those for the same population for the period 1983–1997,11 before any public health interventions (voluntary food fortification and a 1-year statewide awareness campaign) had been implemented. We also present NTD prevalence data in the context of the latest folate awareness data from the Victorian Population Health Survey (VPHS), as this will provide information relevant to monitoring and evaluating the recently approved mandatory flour fortification program in Australia and New Zealand.

This study used high-quality data from a well established population-based register, which included termination data, allowing a much closer estimate of the real prevalence of NTD-affected pregnancies than can be made in countries where termination data are not available.

The most striking finding is the decrease in the prevalence of NTD-affected pregnancies from about 17 to 14 per 10 000 births from 1997 to 1999, coinciding with the introduction of voluntary folate fortification of foods and an awareness campaign. The 3-year moving average was used as a conservative estimate of the effect, taking into account annual fluctuations due to small numbers. Also, it is likely that the impact of voluntary fortification and the campaign would gradually have filtered through to the population over several years, rather than having a sudden effect. The total prevalence of pregnancies affected by NTDs has not decreased further since 1999; rather, the prevalence fluctuates around 13 per 10 000 births. The lack of further decline probably reflects the continuing passive, non-increasing uptake of fortified foods in the absence of a sustained folate-awareness strategy. The apparent increase in NTD prevalence in the 1990s is likely to be the specifically result of increased prenatal detection and notification of anencephalic pregnancies, given that the prevalence of spina bifida or encephalocoele remained fairly constant in the same period (Box 2). The rate of termination for pregnancies affected by NTDs has increased, and there were almost 500 pregnancies terminated because of an NTD during our 9-year study period.

The 18% reduction in both total and birth prevalence of NTDs is far less than the postulated reduction achievable if periconceptional folate intake was optimised.1 The prevalence of NTDs in Victoria (13 per 10 000 births) remains at least double that achieved in countries where mandatory fortification has been in place for a number of years (eg, 6.8 per 10 000 births in Alberta, Canada and 5.6 per 10 000 births in mainland United States).16,17 Part of the approach to achieving further reductions would clearly be to improve individual women’s knowledge of the importance of folate and their adherence to supplementation. The other part of the approach, aimed at the population level, is food fortification. After years of intense debate, a program for introducing mandatory fortification has now been approved for Australia3 and is likely to be supported by the community.18

The VBDR data have shown the relatively increased vulnerability of younger women (younger than 30 years and certainly younger than 25 years) to having a baby with an NTD, with the risk being even higher than in our previous study.11 In the 1983–1997 study, the 20–24-years age group had an odds ratio (OR) of 1.17 (P = 0.09), while the same age group in our study had an OR of 1.70 (P < 0.001). The VPHS data help explain this finding by showing considerable variation in use of and knowledge about folate between age groups, with younger women being less aware and less likely to be taking a supplement. The slight improvement in younger women’s understanding that folate is needed for a pregnancy-related issue, and the fact that more women in this age group are now receiving information from health professionals is encouraging (Box 6).

Maternal epilepsy, another recognised risk factor for NTDs, conferred an increased OR of 1.73 in our study, but this is lower than the OR of 3.70 reported in the previous Victorian study.11 This suggests that awareness of the importance of folate in this high-risk population has improved, probably among women themselves as well as among their health professionals.

The recent VPHS data show an increase in the proportion women taking a daily folate supplement, but overall use remains low at less than 30%. This is similar to 2005 South Australian findings indicating that 30% comply with supplementation in terms of both dose and timing.19 Corresponding figures for Western Australia show a rate of folate supplement use of 29%–45%,20 and the estimated rate among all Australian women of childbearing age is 36%.9

Most women who have any knowledge of folate see it as important for general health, rather than being specifically related to pregnancy. There has been no change in women’s knowledge about the relationship between folate and birth defects, nor in reasons for not taking a supplement.

2 Prevalence of neural tube defects by birth year, 1990–2006

4 Prevalence of babies born alive with a neural tube defect by birth year, 1990–2006