Genetic Screening Now an Option in First-Trimester

Women can now opt for tests to screen for genetic defects in the first trimester of their pregnancy, according to a new opinion issued by a leading organization of a obstetricians and gynecologists.

The non-invasive screenings for chromosomal abnormalities, including Down Syndrome, can be performed as early as 10 weeks into the pregnancy using new ultrasound technologies, says the American College of Obstetricians and Gynecologists, or ACOG.

"The major benefit is that we can now offer a non-invasive, no-risk procedure to detect women at risk of a chromosomal abnormality during the first trimester, enabling them to have a definitive test [known as chorionic villus sampling, or CVS] if they are at risk," says Lauren Streicher, an obstetrician-gynecologist at Northwestern Memorial Hospital in Chicago.

This new technique is valuable to women who want to know of any potential problems earlier in their pregnancy.

According to experts, testing for chromosomal abnormalities during the first trimester is widespread in the United States and is also common in Europe.

"Some obstetrical practices have it as part of their routing screening in all pregnancies," says Mary Murry, director nurse-midwifery services at the Mayo Clinic in Rochester, Minn.

But this is the first time that ACOG — the premier OB/GYN academic body — has sanctioned its use. Traditional screening tests, including amniocentesis, are only available during the second trimester.

How Do the Tests Work?

A woman can have the screenings with a certified ultrasonographer between 10 and 14 weeks into the pregnancy.

The test begins with a high-resolution ultrasound examination that measures the length of the fetus between the crown and rump, used to determine the precise date of pregnancy.

Then, the ultrasonographer examines what is called nuchal translucency, or NT, a measurement at the nape of the fetus' neck, and records the maximum thickness between the skin and soft tissue that overlies the base of the neck. An abnormally increased NT has been shown to be associated with fetuses with certain chromosomal abnormalities.

A sample of the mother's blood is also tested for maternal serum markers for chromosomal abnormalities, known as free b-hCG and PAPP-A.

"The test that is positive for aneuploidy [chromosomal abnormalities] offers the parents time for preparation or the ability to decide to terminate the pregnancy," says Murry. "When the test is positive, it's generally followed by an advanced level ultrasound and amniocentesis."

According to Manuel Porto, professor and interim Chair, Department of Obstetrics and Gynecology at University of California-Irvine, "Negative results should provide patients with peace of mind and require little additional follow up or testing."

Who Can Have The Test?

Although the test is available to all pregnant women, "It can be recommended for women with increased risk for the disorders," says Murry. "This would include women over 35 years of age, family history of fetal aneuploidy and previous affected pregnancies."

Porto says that the new technique is beneficial for women older than 35 years of age, and for women who have had more than one pregnancy, the NT test is "probably the best screening test available."

An ultrasonographer has to be trained and certified before they can perform the new test. And according to ACOG, ultrasonographer training and quality control is essential for accurate NT screening.

For hospitals that already have a trained ultrasonographer, the new opinion won't change their current practices.

"We have routinely offered this test for three years and have had a dramatic decrease in the number of women that have amniocentesis since most women find a 95 percent confidence level to be sufficiently reassuring to forego an invasive test," says Streicher.

The organizations adds that, "Although first-trimester screening for Down syndrome … an option, it should be offered only if certain criteria can be met."

These criteria include that ultrasonographers have appropriate training to perform the test, that women have access to information about the different screening options and receive counseling about their choices, and that access to appropriate diagnostic tests when screen results are positive.

Although there are no risks to the test itself, some experts say that there are reasons to remain cautious about interpreting the results from first-trimester screens.

"There is a high rate of false positives for this test and women should be counseled that the only truly diagnostic test is the amniocentesis and this carries a risk of pregnancy loss of 1 in 200," says Murry.

Some experts also wonder about the overall effect of the test.

"All this effort will not improve the premature delivery rate, the cerebral palsy rate, the operative delivery rate, the maternal complication rate at term," says Ralph Dauterive, chief of OB/GYN, of Ochsner Clinic Foundation in Baton Rouge, La.

Yet, the new view will likely mean that the test will become standard care for pregnant mothers. And according to Porto, older women will benefit the most. "For women greater than 35 years of age who traditionally had CVS or amniocentesis routinely, the benefit [to the test] is high detection with reduced of miscarriage as fewer patients require invasive testing."