Prenatal genetic screening and diagnostic testing are used during pregnancy to check whether a baby may have certain genetic or chromosomal conditions. These tests are offered in the first and second trimesters and range from simple blood draws to more involved procedures.
Knowing what each test does and when it is offered can help you feel more informed as your pregnancy moves forward.
Screening vs. Diagnostic Testing: What’s the Difference?
One of the most important things to understand early in pregnancy is the difference between screening and diagnostic testing.
Screening tests estimate the chance that a baby has a certain condition. They do not provide a diagnosis. A result might come back as “low risk” or “higher risk,” which helps guide whether more testing is needed.
Diagnostic tests go a step further. They can confirm whether a specific genetic condition is actually present. These tests give more definitive answers, but they are also more invasive. That is why they are not done routinely for every pregnancy.
Many patients start with screening because it is less invasive and can offer early peace of mind. Others begin diagnostic testing, especially if they have a family history of genetic conditions or a prior affected pregnancy. There is no single correct choice. The best option is the one that fits your needs.
First Trimester Testing Options
Carrier screening looks at the parents rather than the baby. It checks whether you or your partner carry a gene for conditions like cystic fibrosis or spinal muscular atrophy.
This test works best when done before pregnancy, but it can also be done early in the first trimester. If both parents carry a gene for the same condition, there may be a higher chance the baby is affected.
Non-invasive prenatal testing (NIPT), also called cell-free DNA screening, is a blood test available starting around 10 weeks. It screens for common chromosomal conditions like trisomy 21 (Down syndrome), trisomy 18, and trisomy 13. Some versions also look at sex chromosome differences.
NIPT is very accurate as a screening tool, but it does not provide a diagnosis on its own. A higher-risk result usually leads to a conversation about follow-up testing to confirm.
The nuchal translucency (NT) ultrasound is typically done between 11 and 14 weeks. It measures a small fluid-filled space at the back of the baby’s neck. A larger measurement can point to a higher chance of certain chromosomal conditions. Some practices pair this ultrasound with bloodwork to build an overall risk picture.
For families who want earlier diagnostic answers, chorionic villus sampling (CVS) is available around 10 to 13 weeks. This test collects a small sample of placental tissue to check for chromosomal conditions and certain genetic disorders. CVS can give results sooner than amniocentesis, but it does not screen for neural tube defects, so additional testing may be needed.
