• Maternal-Fetal Medicine

Maternal-Fetal Medicine

Prenatal Diagnosis Tests and Screening FAQs

What is a Prenatal Diagnosis Center?

A facility that has been designated as a State approved Prenatal Diagnosis Center (PDC) undergoes periodic and regular evaluations by the State of California’s Genetic Disease Branch (GDB) to assess and assure competency and skill.

What is a fetal anatomy scan (formerly known as ‘level II sonogram’)?

This is an ultrasound examination of the fetus, usually done at around 20 weeks gestation, where anomalies may be detected by looking carefully at the fetus. It usually takes about 30 minutes and is performed by a skilled sonographer and reviewed by one of our perinatologists, who are recognized by the State of California as experts in assessing fetal ultrasound examinations.

What prenatal tests and screenings are available to determine risk for chromosomal abnormalities, like Down syndrome?

Different types of testing are available for screening and detecting common chromosomal abnormalities. Screening tests will help determine if you are at increased risk for these problems, but diagnostic testing would have to be performed to determine if any of these problems are present. Tests are available at various times between nine (9) and twenty (20) weeks. The following is a short description of the available tests and when they are performed.

Screening Tests:

  • First Trimester Screening involves a fetal ultrasound, performed between 11.5 and 14.0 weeks of pregnancy, and is combined with a blood test performed between 10 to 13 weeks, to indicate if your pregnancy is at a higher chance for Down syndrome or Trisomy 18. Instant preliminary risk assessment is available when the blood test is done one week prior to the ultrasound. 5% of all pregnancies are at risk for these anomalies, and this test detects approximately 85% of them.

  • Second Trimester Ultrasound Screening is an ultrasound examination of the fetus, usually done at around 20 weeks gestation, where anomalies may be detected by looking carefully at the fetus.

  • Second Trimester Serum Screening is a test performed during the second trimester between 15 and 20 weeks gestation. This screening has been considered to be the standard of care for many years. Second trimester serum screening involves measuring four fetal proteins from your blood. It screens for Down syndrome, Trisomy 18, open neural tube defects in the pregnancy, and other less common disorders. Approximately 81% of pregnancies affected with Down syndrome will have an increased risk or a “screen positive” result on a second trimester screening test. This test may be combined with the first trimester to give the most accurate risk of Down Syndrome or Trisonomy 18 detecting about 90% of Down Syndrome fetuses.

  • California Integrated Screening involves an ultrasound and a blood test in the 1st trimester (instant preliminary risk assessment is available when the blood test is done one week prior to the ultrasound), followed by a blood test in the 2nd trimester. Results are reported after each test is performed, and different diagnostic options, such as CVS or amniocentesis, are offered if you have a positive screen result.

Diagnostic Testing

Approximately 5% of patients initially tested will be screen positive, but only a small percentage of these patients will actually have a baby affected with Down syndrome or Trisomy 18. If a screening test is abnormal (screen positive) indicating an increased risk of having a baby with either a chromosome problem or an open neural tube defect, you will be offered genetic counseling along with diagnostic testing for a definitive diagnosis. There are two diagnostics tests commonly offered:

  • Chorionic villus sampling (CVS) is performed between 10.5 and 13.5 weeks of pregnancy. CVS is performed by removing a small amount of placental tissue, either transabdominally or transvaginally, which is used to test for chromosome problems. The risk of miscarriage is approximately 1 in 300.
  • Amniocentesis is offered between 15 and 22 weeks of pregnancy. Amniocentesis involves removing a small amount of fluid surrounding the baby. Cells from this fluid are used to test for chromosome problems as well as open neural tube defects and other inherited problems. Amniocentesis is associated with a risk for miscarriage of 0.2%.

Is there pain associated with an amniocentesis?

Most patients experience a small amount of discomfort. This usually lasts a few seconds. Some women experience mild lower abdominal cramping immediately after the procedure.

How long does it take to get the results of an amniocentesis?

Results are typically available in 10-14 days. A member of our staff will call you with the results. (Please be sure we have your most current contact information.)

How long does it take to get the results of a CVS (chorionic villus sampling) procedure?

Results are typically available in 10-14 days. A member of our staff will call you with the results. (Please be sure we have your most current contact information.)

Are there any side effects or limitations after an amniocentesis?

Mild abdominal pain or cramping is normal, as is a small amount of spotting with a transvaginal CVS.

What should I do if I think I am having a problem after an amniocentesis or CVS procedure?

If you experience increasing abdominal pain, fever, chills, vaginal bleeding beyond a small amount of spotting, or leakage of fluid per vagina, you should contact your pregnancy care provider as soon as possible, as this may be the sign of an infection.

Having a baby involves many complex decisions that are best made on an individual basis. There is no one correct answer for all women.

Please understand that a normal chromosome result does not guarantee a healthy baby.

If you have further questions or would like to be scheduled for a genetic consult to evaluate the genetic risks in your pregnancy, please speak to your referring OB provider, or call our offices for more information.