Antenatal screening for Down syndrome

A report released in April 2007 by the National Screening Unit recommends important changes to improve the quality and safety of the current approach to antenatal screening for Down syndrome in New Zealand.

Antenatal Down Syndrome Screening in New Zealand 2007 is the result of work carried out by the Antenatal Down Syndrome Screening Advisory Group, which was convened as part of a review of the current practice of antenatal screening for Down syndrome undertaken by the National Screening Unit.

The Advisory Group unanimously agreed that the current practice of screening using only maternal age and/or nuchal translucency (NT), without biochemical markers is unsafe, inequitable, and should not continue. It said current screening methods commonly used are not as reliable and accurate as other methods that are available. This results in too many women having diagnostic tests, and as these have a small risk of miscarriage (about 1 to 2 percent), pregnancies are being lost unnecessarily. The Advisory Group made a number of recommendations for ways to improve the safety and quality for antenatal Down syndrome screening.

The Minister of Health, Hon Pete Hodgson, has requested further work to be carried out to look at how a nationally-organised screening programme for antenatal Down syndrome could be implemented. This will be completed by October 2007.

The primary intention of a national screening programme would be to improve the quality and safety of screening practice. A national screening programme would include an informed consent process, national standards, monitoring and evaluation.

Assessment of current antenatal Down syndrome screening

The National Screening Unit commissioned Professor Peter Stone from the University of Auckland, to carry out an assessment of current antenatal screening for Down syndrome in New Zealand. Professor Stone's February 2006 report, Assessment of Antenatal Screening for Down Syndrome in New Zealand, made a number of recommendations to the National Screening Unit.

While it was considering these recommendations, the Ministry of Health wrote to health practitioners with advice about how the current concerns about Down syndrome screening could be addressed. The letter was sent to radiology and laboratory services, midwives, general practitioner, and obstetricians. A media statement about the issues was also released.

Read the letter to health practitioners "Antenatal screening for Down Syndrome"

Read the media release "Down Syndrome antenatal screening under review", 8 June 2006

What is Down syndrome?

Down syndrome is a genetic condition that causes delays in physical and intellectual development. It is a relatively common condition, with a population incidence of about 1 in 1000 live births. As a congenital condition (present from birth) it has lifelong implications that include intellectual and growth impairment and a range of other possible medical complications.

Most children with Down syndrome are born to women under 35 years of age, as this is when most women have children. However, the chance of having a child with Down syndrome increases quite steeply for an individual woman from around 35 years of age onwards.

Screening for Down syndrome

Antenatal screening can estimate for each woman her chance of having a child with Down syndrome.

The antenatal screening tests available in New Zealand are:

an ultrasound scan at about 12 weeks gestation, using Nuchal Translucency (this is publicly funded), and
a second trimester blood test, usually done between 15 and 20 weeks of gestation (this is available but is not publicly funded. The cost is approximately $75 for this test).

Any woman receiving a positive screening test result should be provided with adequate post-test information and discussion, and offered a diagnostic test (amniocentesis or CVS). Both these diagnostic tests are invasive and carry a small risk of fetal loss (0.5 to 1 percent).