Some families would like to know if their baby is at an increased risk for a chromosome problem such as Down Syndrome, or Trisomy 21. This disorder is the most common chromosome difference for liveborn babies and a common cause of intellectual disability. There are different types of tests that can inform families of increased or decreased risk. All testing is optional, and your choices can be tailored to your family after discussing with your doctor, our perinatology team, or a genetic counselor.

Different options for testing can include:

• Early fetal anatomy: an ultrasound examination at 11 to 14 weeks that looks at how the baby is coming including a nuchal translucency measurement. At San Diego Perinatal our sonographers are trained to look closely to see if there are any early clues for birth defects or chromosome differences. Increased nuchal translucency measurements can happen in normal fetuses but also flag pregnancies as being at higher risk for chromosome differences, genetic disorders, or fetal heart defects. In this situation, additional counseling and testing is offered.
• The state of California has used biochemical screening for many years. Currently, the state program utilizes a single marker, MSAFP to screen for neural tubal defects. This screening is a maternal blood test available between 15 and 21 weeks.
• In 2022, the state of California began offering cell-free DNA screening to detect pregnancies at increased risk for the most common chromosome abnormalities. In 2024, they are adding screening for sex chromosome abnormalities. This blood test, sometimes referred to as NIPT, will screen for trisomies 21, 18 and 13. It will also screen for extra or missing sex chromosomes. This test can be performed any time after 10 weeks gestation and is a maternal blood test.

Frequently Asked Questions

What if it is not possible to measure a nuchal translucency?
For technical reasons or due to the gestational age of the pregnancy, some pregnant women will not be able to have a nuchal translucency measurement. A first trimester or early second trimester anatomy scan is valuable because it is also an early anatomy scan in which many birth defects can be detected.

What if my screening test comes back positive?
If your cell free DNA or NIPT screening test comes back positive for any abnormality, you should be referred for follow-up services including: genetic counseling, a comprehensive anatomy scan and a conversation about your screening and testing options with a perinatologist.

Cell free DNA is a screening test and there can be normal pregnancies that test positive and, more rarely, abnormal pregnancies that are missed. At San Diego Perinatal Center, we recommend genetic counseling and confirmation with amniocentesis or chorionic villus sampling to give you the most accurate information after a positive screening test.

We can help arrange appropriate follow up services and answer additional questions.