Neural tube defects in Australia - An epidemiological report

Neural tube defects in Australia

Neural tube defects (NTD) are major congenital anomalies that result from very early disruption in the development of the brain and spinal cord. NTD are described under three main categories in this report: anencephaly, which is the absence of a major part of the brain, skull and scalp; encephalocele, which is a protrusion of brain tissue and/or its covering membranes through a defect in the skull; and spina bifida, in which the vertebrae that cover the spinal cord have one or more openings in the middle, allowing exposure and/or protrusion of nervous tissue and coverings with various degrees of damage to nerves.

During last few decades, studies have shown mounting evidence of a decreased prevalence of NTD with increased intake of folic acid during the period around conception. Folate is necessary for the production and maintenance of new cells, which is especially important during periods of rapid cell division and growth such as pregnancy. Australia actively promoted the increased intake of folic acid among women of child bearing age for more than a decade with the intension of decreasing the prevalence of NTD. As a result there was a reduction in the prevalence of NTD affected pregnancies, but this was not equal among all groups of women. From September 2009 onwards, Australia will join many other developed countries in implementing mandatory folic acid fortification of bread making flour, in an attempt to further reduce the prevalence of NTD. The information provided in this report is expected to assist in evaluating the impact of mandatory folic acid fortification in the future.

This report describes the current prevalence of NTD and the trends during the past decade. Characteristics and outcomes of the births and demographic and pregnancy characteristics of the mothers are presented for the period 1998–2005. Information on terminations of pregnancy before 20 weeks gestation is also presented for four jurisdictions where such data are available: New South Wales, Victoria, South Australia and Western Australia.

Key findings:

There were a total of 944 births affected by NTD from 1998 to 2005. Of these births, 523 were live births and 421 were fetal deaths (still births and terminations after 20 weeks gestation). This equates to a prevalence of neural tube defects (NTD) among births of 4.6 per 10,000.
There was no significant decrease in NTD among births during the period 1998–2005, despite early diagnosis, health education and health promotion programs and voluntary fortification of food with folic acid.
While there has been little change in the prevalence of NTD amongst births, there has been a decrease in the overall prevalence of NTD (taking into account births as described above as well as pregnancies that may have been terminated before 20 weeks gestations due to early detection of an NTD). Results from the four states that include these data indicate that during 1998–2005 there were a total of 1,657 pregnancies affected by NTD in these four states. Of these pregnancies, 903 were terminated prior to 20 weeks gestation. The overall prevalence of NTD in these four states, including early terminations, was more than twofold higher (10.1 per 10,000 pregnancies in 2005) than the prevalence at birth. This represents a 32.7% decrease over the 14 years between 1992 and 2005. However, the prevalence based on four states is also likely to be an underestimate.
Data from the four states for the period 1998–2005 reveal that more than 77% of pregnancies affected with NTD were fetal deaths or were managed by pregnancy terminations.
The three states that collect near complete data show a higher prevalence of NTD compared with the prevalence in four states.
Younger women are more likely to have NTD-affected pregnancies than older women: teenage women had the highest rate and women aged 30–34 years the lowest.
The rate of pregnancies affected with NTD was higher for women living in remote areas than for women living in major cities.
Multiple pregnancies were more likely to have NTD than singleton pregnancies.
Indigenous women had a higher rate of NTD-affected pregnancies than non-Indigenous women.
The prevalence of NTD in Australia was similar to or slightly higher than other developed countries.
At least 50% of the pregnancies with NTD were terminated before 20 weeks gestation. Hence, collection of data on early terminations is critical in reporting the accurate prevalence of NTD.