Prenatal screening and diagnostic tests
There are two kinds of prenatal tests:
- Screening tests can tell if your baby might be at risk of a genetic problem or birth defect, but can’t tell for sure if your baby has a problem. If your screening test shows that your baby is at risk, you may want to have a diagnostic test.
- Diagnostic tests can tell with much greater accuracy if your baby actually has a genetic problem.
Please use the following chart as a guide. Your doctor will give you more specific guidelines on the prenatal screening and diagnostic tests you might need to make sure you are healthy and that your baby is developing normally. Some of these tests are given routinely, others only in certain situations.
If your test results show you or your baby are at risk of a problem, you may be offered genetic counseling and further testing.
Screening tests
| Type of test | What test screens for | When usually done |
| Genetic carrier tests | To see if you or your partner carry a genetic mutation that may cause a disorder such as cystic fibrosis, Tay-Sacks, or sickle cell anemia | First trimester |
California Prenatal Screening Program (CPSP): 3 options
|
Down syndrome, trisomy 18, open neural tube defects, abdominal wall defects, and Smith-Lemli-Opitz syndrome | 1st blood test between 10 weeks and 13 weeks, 6 days
ultrasound between 11 weeks, 2 days and 14 weeks, 2 days 2nd blood test between 15 and 20 weeks
same as above but without the ultrasound
single blood test between 15 to 20 weeks |
| Non-invasive prenatal testing (NIPT) | Down syndrome, trisomy 18, and trisomy 13 | As early as 10 weeks |
| Ultrasound | Birth defects and other findings possibly related to genetic disorders | Between 18 and 20 weeks |
Diagnostic tests
| Type of test | What test screens for | When usually done |
| Chorionic Villus Sampling (CVS) | Down syndrome and other chromosomal problems | Between 10 to 14 weeks |
| Amniocentesis | Down syndrome and other chromosomal problems; genetic conditions; and open spine and abdominal defects | Between 15 to 20 weeks |
By Betty Shen, MD - Published November 3, 2015
