First Trimester Screening

First Trimester Screening is an earlier non-invasive way for women to screen for Down syndrome during pregnancy. Through the combination of a special ultrasound examination and a simple blood test, First Trimester Screening identifies pregnancies that have an increased risk of having a baby with certain chromosome abnormalities, such as Down syndrome, during the first trimester of pregnancy. Patients must be between 10 ½ and 13 weeks, 6 days of pregnancy to have the First Trimester Screening performed. The optimal time to have the screening performed is between 10 ½ to 12 weeks of pregnancy. Women ages 35 and over should be offered diagnostic testing, such as chorionic villus sampling or amniocentesis based on age-related risk alone.

Procedure:

• Ultrasound: The ultrasound is typically performed on the abdomen, although in some cases it may be performed transvaginally. This form of testing is non-invasive, meaning there is no risk of harming the baby. During the ultrasound, the gestational age is estimated. During the ultrasound, a measurement is taken of the thickness of the back o f the baby’s neck. This thickness is also referred to as the nuchal fold thickness or NT measurement. Studies have show that 80% of babies with chromosome problems, have an increased nuchal thickness. An increased NT measurement can also be associated with heart problems and other genetic conditions.
• Blood Test: A blood test is performed on the mother to measure the level of three proteins that are normally found in a woman’s bloodstream during pregnancy. The levels of these proteins may indicate an increased or decreased risk of the fetus having chromosome abnormalities. The proteins that are measured are:
• Pregnancy-associated plasma protein A (PAPP-A)
• Free beta subunit of human chorionic gonadotropin (bHCG)
• Alpha feto-protein (AFP)

Screening Results and Accuracy:

By combining the results of the ultrasound and blood test along with the age, race and weight of the mother, a number can be generated by computer which represents the risk of the pregnancy being affected by Down syndrome or another chromosome problem. Experience has shown that, together, the ultrasound and blood screen will identify approximately 90% of babies with chromosome abnormalities.

Test results are typically available within one week of the screening. If the results indicate an increased risk for a chromosome problem, an appointment with a genetic counselor or physician will be offered. Chorionic villus sampling and amniocentesis will be made available for the diagnosis of a chromosome problem.

Advantages of First Trimester Screening:

• Allows for earlier detection of an increased risk for Down syndrome and other chromosome abnormalities, during pregnancy.
• If the screening test indicates an increased risk, chorionic villus sampling (CVS) can be performed in the first trimester of pregnancy to determine if the baby has a chromosome problem. This allows for more time for counseling and decision-making by the couple prior to when the woman is “showing”. In addition, pregnancy termination is generally safer in the first trimester of pregnancy, should this be an option for the couple.
• If the screening test does not indicate an increased risk, this allows some reassurance to the couple earlier in the pregnancy.
• Based on preliminary evidence, First Trimester Screening can detect a higher percentage of babies with Down syndrome than the currently available second trimester screening test (MSAFP or triple screen test).

Risks:

As with any test, if a woman receives a result which indicates an increased risk, her anxiety about the pregnancy may increase. Studies show that approximately 5% of women having this test have abnormal results, indicating an increased risk for a chromosome problem. Women receiving abnormal screening results will be offered prenatal diagnosis to determine if a chromosome problem is present. These procedures (chorionic villus sampling and amniocentesis) each carry a risk for miscarriage.

Screening Summary:

• Early detection of an increased risk for carrying a baby with Down syndrome or other chromosomal disorders which allows more time for decision making, including the option of first trimester prenatal diagnosis.
• Better detection rate (90% versus 60 -70%) than Second Trimester Screening for Down syndrome and other chromosomal disorders.
• The ultrasound can identify some babies at risk for heart defects or other genetic conditions.
• If the results show an increased risk, several testing options exist for the diagnosis of chromosome problems.
• This testing poses no risk to the baby.

Next Steps:

Please contact our genetic counselors at 773-472-4900 for further information regarding First Trimester Screening or e-mail us with any questions or inquiries.