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Deborah Wing, M.D.
Perinatologist

From the moment a woman learns she’s pregnant, the well-being of her fetus is an ongoing concern. Will the baby be healthy—or have congenital abnormalities, Down syndrome or other chromosomal problems?

A new, noninvasive test conducted early in pregnancy can answer some of these questions. Called the combined first-trimester screening (CFTS), it assesses a fetus’s risk for Down syndrome and trisomy 18. Both conditions are chromosomal defects that cause mental and physical abnormalities.

The screening involves a simple blood test and special ultrasound around the eleventh week of pregnancy. The blood test looks for abnormal levels of a specific protein and hormone associated with these birth defects, while the ultrasound scan examines the fluid under the skin of the fetus’s neck. The thicker the fluid, the greater the chance of Down syndrome and trisomy 18.

Before CFTS became available, women in the first 12 weeks of pregnancy had access to only one test that could detect these problems. But the test, chorionic villus sampling (CVS), is invasive and poses a risk of miscarriage. Amniocentesis—another option—is typically performed later in the pregnancy. It is also invasive and carries a chance of infection or miscarriage.

CFTS identifies about 90 percent of fetuses with these two chromosomal defects. If the results are positive, further diagnostic testing is recommended to confirm findings.

The new screening is considered a risk assessment for Down syndrome and trisomy 18—not a definitive diagnosis. In the past, only women over 35 were tested for these birth abnormalities. CFTS reduces reliance on the mother’s age as the only predictor of Down syndrome. The screening will allow many younger women, who actually have the majority of Down syndrome babies, to know if their fetuses are at risk without having invasive testing.

First-trimester screening offers many advantages over testing done later in pregnancy. CFTS has lower false-positive rates and higher Down syndrome and trisomy 18 detection rates than second-trimester alpha-fetoprotein (AFP) screening. AFP is a blood test used to identify Down syndrome, trisomy 18 and problems with the fetus's spine and digestive system. Additionally, because CFTS poses no risk, it’s especially valuable for those who have tried to get pregnant for a long time or are concerned about the possible outcomes of invasive procedures.

UC Irvine Medical Center is one of only a few hospitals in Orange County to offer CFTS with specially trained and certified sonographers and physician sonographers.

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