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 60 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 9 and 20 weeks. The following is a short description of the available tests and when they are performed.

Screening Tests:

• Non-invasive prenatal screening(NIPT)/cell free DNA(cfDNA) is a blood test available starting at 10 weeks gestation that determines whether your pregnancy is at a high risk for Down syndrome (Trisomy 21), Trisomy 18 and Trisomy 13. It can also determine the baby’s sex. There is an option available at specific laboratories to screen for a few additional conditions, such as sex chromosome abnormalities or microdeletion syndromes. The likelihood of your child being affected (true positive rate) is less for these add-ons than for the “core” trisomies (21, 18 and 13). Cell free DNA can detect over 99% of Down syndrome, Trisomy 18 and Trisomy 13. The genetic counseling team at our clinic can help you decide which test to pursue.

• First Trimester Ultrasound is a fetal ultrasound performed between 11.5 and 14.0 weeks of pregnancy. It measures a space of fluid at the back of the fetal neck, which can help identify chromosome abnormalities, heart defects and certain genetic conditions. This scan is also useful for identifying major brain or limb anomalies. It is recommended in all pregnancies, even if the pregnant person has already had low-risk blood screening
  
  
• Second Trimester Ultrasound Screening or Detailed Anatomy Ultrasound is an ultrasound examination of the fetus, usually done at around 20 weeks gestation. The ultrasound technicians screen for anomalies by measuring and imaging specific parts of the fetus. The physician discusses the results of the ultrasound with the patient following their scan.
  
  
• Second Trimester Serum AFP Screening is a test performed during the second trimester between 15 and 21 weeks gestation. Second trimester serum screening measures alpha fetoprotein (AFP) in the pregnant person’s blood. It screens for open neural tube or abdominal wall defects in the pregnancy but can also indicate an increased risk of adverse outcomes. If this test is abnormal, fetal ultrasound and amniocentesis are the next available evaluations.
  
  

Diagnostic Testing

Diagnostic tests are the most accurate genetic evaluations available during pregnancy, though there is a small risk of pregnancy loss associated with these tests (see below). There are two diagnostic tests commonly offered:

• Chorionic villus sampling (CVS) is performed between 11 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 genetic or chromosomal abnormalities. The test is done under ultrasound guidance. The risk of miscarriage following this procedure is approximately 1 in 400 (0.25%).
• Amniocentesis is typically offered between 16 and 23 weeks of pregnancy. Amniocentesis involves removing a small amount of fluid surrounding the baby. Cells from this fluid are used to test for genetic or chromosomal abnormalities, as well as neural tube defects. The test is done under ultrasound guidance. The risk of miscarriage following this procedure is approximately 1 in 900 (0.11%).

 

Why do patients consider diagnostic testing like amniocentesis or CVS?

There are many reasons to consider diagnostic testing. Some patients will pursue this testing when a previous screening test is abnormal (screen positive), indicating an increased risk of having a baby with a genetic or chromosomal abnormality or an open neural tube defect. Other patients considering CVS or amniocentesis have a family history of a specific genetic condition or have had an abnormal fetal ultrasound during their pregnancy. Some patients opt for these tests based on maternal age. All patients considering diagnostic testing are offered genetic counseling in our office to discuss whether the test is right for them.

Is there pain associated with an amniocentesis or CVS?

Most patients experience a small amount of discomfort, such as pressure or cramping, during the procedure itself. 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 following a diagnostic procedure like CVS or amniocentesis?

Results are typically available in 8-10 days, but certain genetic testing can take several weeks to produce a result. A member of our genetic counseling team will discuss turnaround time for each test at the time of the procedure. A genetic counselor will then call you with the results when they are available. (Please be sure we have your most current contact information.) 

Are there any side effects or limitations after an amniocentesis or CVS?

Mild abdominal pain or cramping is normal, as is a small amount of spotting with a transvaginal CVS. We recommend that you avoid strenuous activity for 48 hours after a procedure. Activities to avoid include lifting over 10 pounds, intense physical exercise, air travel, anything inside the vagina, and immersion in water (no swimming or baths). 

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 these may be signs of an infection. We provide our patients with instructions following their procedure, so they know who to call with questions or concerns. If you cannot reach your own physician or if they instruct you to call us, our main office phone number (510-597-1863) can connect you with our physicians. If your call is after standard business hours, an answering service can assist you in reaching our doctors.

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 consultation to evaluate the genetic risks in your pregnancy, please speak to your referring OB provider, or call our offices for more information.