Neural tube defects in Australia

Back to the report Neural tube defects in Australia

Summary

About this report

This report describes the current prevalence of neural tube defects (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.

Among other things, this report provides baseline prevalence data for NTD in Australia, prior to the implementation of mandatory folic acid fortification of bread flour in September 2009. It is expected that the information provided will assist in evaluating the effect of mandatory folic acid fortification in the future.

This report was compiled at the request of the Statistical Information Management Committee (SIMC) of the Australian Health Ministers Advisory Council, using the data collected by the Australian Congenital Anomalies Monitoring System (ACAMS), which is the national data collection of congenital anomalies. State and territory birth defect registries and perinatal data collections provide data on congenital anomalies to ACAMS.

What are neural tube defects?

Neural tube defects are major congenital anomalies that result from very early disruption in the development of the brain and spinal cord. There are three distinct forms of neural tube defects described 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.

How is folic acid connected with NTD?

Since the 1960s there has been mounting evidence of a decreased prevalence of NTD with increased intake of folic acid during the period around conception. Folic acid and folate (the anionic form) are forms of Vitamin B. Folic acid and folate occur naturally in food; folic acid may be added to some foods and can also be taken as a supplement. 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 infancy and pregnancy.

Over the past decade Australian governments have actively promoted folic acid intake around the time of conception in an attempt to reduce the prevalence of NTD. From September 2009 onwards, Australia will join many other developed countries in having mandatory folic acid fortification of flour for bread making, in an attempt to further reduce the prevalence of NTD.

How many NTD are there in Australia?

This report presents the prevalence and trends of births with NTD for all jurisdictions in Australia, except Northern Territory, from 1998-2005. Main findings include:

• There were a total of 944 births over this period affected by NTD. 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. However, the prevalence based on four states is likely to be an underestimate. 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.
• 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.

Other findings include:

• 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.

What is needed for future reporting?

As at least 50% of the pregnancies with NTD were terminated before 20 weeks gestation, collection of data on early terminations is critical in reporting the accurate prevalence of NTD.

A program of national data development is underway with the aim of developing a national minimum data set (NMDS) for congenital anomalies, with the expectation of providing high quality national data on congenital anomalies.

This will be vital for evaluating the effectiveness and outcomes of mandatory folic acid fortification of bread making flour.