A new antenatal screening test has not had the high uptake expected, a study published in the New Zealand Medical Journal reveals.
Only 51 per cent of pregnant women surveyed had undertaken the new screening test for Down syndrome and other chromosomal anomalies in their first trimester.
The new test, introduced in 2010, involves a blood test and an ultrasound scan, rather than just an ultrasound.
The research was conducted in Canterbury between February 2009 and January 2010, before the new screening test was in place, and between May 2010 and April 2011, after it was introduced.
The data showed only 51 per cent of women had undertaken the new screening test after it was introduced.
The study's authors - among them obstetricians, gynaecologists and midwives at Canterbury DHB - said they had expected a higher rate of uptake.
"We anticipated that there would be a high uptake of screening by women in Canterbury," the report said.
"This study does not assess the reason for the low level of uptake; for example whether women are informed and chose not to undertake the screen or whether they are not aware of this offer."
The authors noted that improved antenatal screening programmes had increased screening uptake in parts of Britain and they had hoped to see the same here.
In 2005, the National Screening Unit commissioned Professor Peter Stone and Diana Austin to assess antenatal screening for Down syndrome.
Until 2010, women were offered a nuchal translucency (NT) measurement done by ultrasound scan at the end of the first trimester.
The scan measures fluid behind the neck of the fetus and could be performed by a sonographer with a certain level of expertise.
In 2010, a new screening programme of a blood test and an NT scan was deemed the best practice for screening. It has a detection rate of 83 to 86 per cent.
If the screening shows a woman has an increased risk of a chromosomal anomaly, she is then offered invasive testing.