The Down syndrome birth rate has significantly decreased with the introduction of screening tests from 22.28 per 100,000 live births in 2001 to 7.79 in 2010, the Taiwan Society of Perinatology said yesterday, urging all pregnant women to undertake the recommended tests.
The incidence of Down syndrome was 7.92 per 10,000 births between 2001 and 2010, which means that there was one infant born with the disorder in every 1,263 live births, according to the group, which said that the incidence increases with the age of the pregnant woman, with 1 in every 385 live births for pregnant women who are 35.
“The incidence rate for pregnant mothers aged 23 is about one per 1,000 to 1,500,” society president Tsai Ming-sing (蔡明松) said. “With advancing age, at 40, the risk increases to 1 in 100.”
A research team led by attending physician of obstetrics at National Taiwan University Hospital (NTUH) Lee Chien-nan (李建南) found that there is a positive impact of Down syndrome screening on Taiwanese births.
The second-trimester — 15 to 20 weeks — double test (AFP test and B-hCG test) was introduced to Taiwan in 1994 and has a detection rate of 60 percent; the test reduced the ratio of live-born to total Down syndrome occurrence (registered live births and still births) from 70.42 percent in 1994 to 48.74 percent in 2001, according to the team.
The ratio has further decreased to 25.88 percent in 2006, said Lee, when the first-trimester (10 to 13+6 weeks) screening, or nuchal translucency scan, was widely introduced in Taiwan.
However, as some pregnant women take a screening test only when they are in the second trimester of pregnancy, and as the detection rate of the second-trimester double test is not satisfactory, since 2008 the second-trimester quadruple test (with the addition of two more markers, uE3 and Inhibin A) has been used and has increased the detection rate to 81 percent.
The combination of the first and the new second trimester tests has decreased the ratio of live-born to total Down syndrome occurrence to 20.64 percent in 2008 and to 5.99 percent in 2010.
Obstetrician Lin Shin-yu of NTUH’s Hsin-Chu Branch, a co-author of the research, said that the amniocentesis, or amniotic fluid test (AFT), is very accurate in detecting the condition and is recommended by Taiwan’s health authority for pregnant women aged 35 years and over, despite some drawbacks.
“It has a risk of miscarriage of one to three per 1,000 due to its invasive character,” Lin said.
“AFT is also much more expensive,” Lin said.