Prenatal Genetic Screening
The purpose of genetic screening is to identify risk for birth defects. These defects are often caused by chromosomal abnormalities, in which there can be an absent or extra chromosome. Birth defects can affect a baby’s appearance, body function, and development. Screening tests can assess the baby’s risk of having Down syndrome and other chromosomal problems, as well as neural tube defects. If a screening test shows an increased risk of a birth defect, diagnostic tests may be done to determine if a specific birth defect is present.
Although screening tests are offered to all pregnant women, it is your choice to have them done. Knowing whether you baby is at risk of or has a birth defect beforehand allows you to prepare for having a child with a particular disorder and organize the medical care your child may need. At El Camino Women’s Medical Group, our goal is to help you determine if your baby is at increased risk of birth defects, and to offer you the appropriate testing with which you are comfortable.
Sequential Integrated Screening:
This combines results from a first trimester and second trimester screen. The overall detection rate for Down Syndrome is 94-96%.
First trimester screen: combines a 1st trimester blood test (10 weeks – 13 weeks 6 days) and ultrasound (Nuchal translucency, NT at 11-14 weeks). This is a special ultrasound performed by clinicians with special training. It measures the back of the baby’s neck. 1st trimester screen alone has a detection rate of 82-87%.
Second trimester screen(Quad screen): blood test drawn at 15- 20 weeks. If the 2nd trimester screen is done alone (no first trimester screen) it has a detection rate of 81%.
With high quality ultrasound we are able to identify birth defects that my require attention before or after birth. The second trimester anatomy scan, typically done between 18-20 weeks, is a detailed ultrasound examining fetal anatomy. Views obtained include the fetal head and spine, chest, heart, abdomen, and urinary tract. Fetal gender is also evaluated.
Non-invasive Prenatal Testing (NIPT):
Also known as cell-free DNA, fetal DNA can be isolated from the mother’s blood as early as 10 weeks during pregnancy. With good accuracy it can test for Trisomy 21 (99%), Trisomy 18 (99%), Trisomy 13 (92%), and sex chromosomes (99%) to determine sex-chromosome related disorders and also to report gender. Certain enhanced tests for high-risk patients can also screen for microdeletions responsible for rare, hereditary syndromes. While results of this testing are highly accurate (99%), a negative test result does not ensure an unaffected pregnancy, and not all chromosomal abnormalities can be tested. Patients who receive a positive result will be referred for genetic counseling and diagnostic testing. Lab names for NIPT include MaterniT21, VisibiliT, Counsyl Informed Pregnancy Screen, Panorama, and Harmony.
For those patients that elect to perform NIPT, it replaces the need for 1st trimester screening. 2nd trimester screening is still recommended due to its additional risk assessment for neural tube defects and a rare metabolic disease.
NIPT has increasingly become the norm for genetic screening, even in low risk women. We order it as a routine on all patients in all pregnancies and make sure to use the most cost effective lab for your testing. Most insurance carriers now cover this test for all pregnancies and the cost to patients is less than previous first trimester screening: on average and NT plus blood screening costs $800-900, NIPT on average costs about $700. Remember, it is the more accurate test.
When there is a coverage issue, we will work with you to appeal through your insurance or to work with the laboratory to manage the costs. If you have any trouble, reach out to our office manager.
Diagnostic Tests (invasive): Amniocentesis (15-20 weeks): A procedure in which a needle is used to withdraw and test a small amount of amniotic fluid and cells from the sac surrounding the fetus. There is a small chance of miscarriage (1 in every 400 procedures)
Chorionic villus sampling, CVS (10-14 weeks): A procedure in which a small sample of cells is collected from the placenta. There is a similar chance of miscarriage compared to amniocentesis when performed by an experienced provider.
Diagnostic tests are 100% accurate for the chromosomal tests they perform.