Physicians Study Improved Fetal Screening for Down Syndrome
Physicians at Thomas Jefferson University Hospital are leading a national study to see whether blood tests and a specific ultrasound measurement can offer expectant parents a more accurate assessment of the risk of Down syndrome in the first trimester of pregnancy.
While this new screening approach does not definitively diagnose a fetus with Down syndrome, it does establish an accurate risk level, explains Ronald Wapner, MD, Professor of Obstetrics and Gynecology at Jefferson Medical College (JMC) and co-principal investigator of the National Institute of Child Health and Human Development-funded project. This provides parents with information to help them decide whether to pursue further testing, including chorionic villi sampling (CVS) or amniocentesis.
Early results have been extremely promising.
Approximately 80 to 90 percent of at-risk pregnancies have been successfully identified using the new screening test, says Dr. Wapner. This high detection rate can be very reassuring to mothers whose screening test results show a low risk.
The current screening blood test for Down syndrome, known as the triple screen, measures the levels of three proteins: Beta-hCG, estriol, and alpha-fetoprotein. But the triple screen, not done until 16 to 18 weeks of pregnancy, detects only 60 to 70 percent of fetuses with Down syndrome. Women who test positive can choose amniocentesis to confirm the result.
Amniocentesis and CVS both carry risks. The benefit of the new test is the earlier gestational age and the higher predictive accuracy, notes Dr. Wapner.
About the study.
The First Trimester Maternal Serum Biochemistry and Nuchal Translucency Screening Study hopes to recruit 100,000 pregnant women at 13 medical centers throughout the United States. Study results are due next year. Dr. Wapners co-principal investigator is Laird Jackson, MD, Professor of Medicine, JMC. The screening is more complex than the triple screen. The study uses a new, standardized ultrasound technique to measure embryonic nuchal membrane thickness as well as blood tests.
The blood tests measure beta-hCG as does second trimester screening and also uses pregnancy-associated plasma protein A (PAPP-A), which was recently found to be decreased in women carrying fetuses with Down syndrome. An ultrasound is done to measure nuchal translucency the thickness of a membrane at the back of the neck of a developing fetus. An abnormally large nuchal (neck) fold, may indicate a greater risk of Down syndrome.
Its technically more difficult since the blood tests have to be sent for special analyses, and the nuchal membrane ultrasound has to be done in a very precise, specific way, which requires special training, explains Dr. Wapner. The ultrasound method will not be widely available until more ultrasound specialists can be trained.
Calculating fetal risk of Down involves other variables. The age of the mother and her pregnancy history, in addition to the blood test and ultrasound results, are factored into the equation, explains study coordinator Maureen McGee, RN, BSN, in the Department of Obstetrics and Gynecology, JMC. Women whose risk is greater than 1 in 270 are considered high risk and will be offered genetic counseling.
The clinical trial will also compare, in those women at risk, the safety of using amniocentesis or CVS in diagnosing Down syndrome between 13 and 15 weeks of pregnancy. The researchers seek to learn how efficient and sensitive the new screening is, and how women accept screening results and use the information they receive, Dr. Wapner says.
Even if the study confirms the preliminary findings, it might not change the way most women are screened for Down syndrome at least not right away. Education, appropriate training and counseling are needed. Women need to know that this new group of tests may represent an improvement over a system that they are already using widely. It can be used earlier, and can also detect other abnormalities, like heart defects, says Dr. Jackson.
While it is too soon to know for sure if the new screening methods can effectively predict Down syndrome, the researchers are hopeful. If first trimester screening continues to be as efficient as it is looking, it likely will replace second trimester screening as standard,Dr. Wapner says. Thats extremely important. Patients will have more time to decide what to do with the information.
Jefferson is one of 13 medical centers throughout the nation the only center in the Delaware Valley enrolling women in the Down syndrome screening study. Most women who are pregnant between 10 and 14 weeks based on the first day of the last menstrual period are eligible. For more information, call Jeffersons Down Syndrome Screening Center at 215-955-4296.