The Most Important Distinction: Screening vs. Diagnostic

Before diving into specific tests, there is one concept that changes how you interpret every result: the difference between screening and diagnostic testing.

Screening tests estimate the probability that a condition is present. They tell you whether risk is higher or lower than average, but they cannot confirm or rule out a diagnosis. A "high-risk" screening result does not mean your baby has a condition. It means further evaluation is warranted.

Diagnostic tests give a definitive yes-or-no answer with greater than 99% accuracy. They analyze actual fetal cells or DNA. The tradeoff is that diagnostic tests are more invasive.

Understanding this distinction prevents a tremendous amount of unnecessary fear. A screening result is not a diagnosis.

NIPT (Non-Invasive Prenatal Testing)

What It Is

NIPT, also called cell-free DNA screening, is a blood draw from your arm. It analyzes fragments of placental DNA circulating in your bloodstream. No needle goes near your uterus.

What It Screens For

NIPT primarily screens for:

  • Trisomy 21 (Down syndrome): detection rate above 99%
  • Trisomy 18 (Edwards syndrome): detection rate around 96-98%
  • Trisomy 13 (Patau syndrome): detection rate around 91-93%
  • Sex chromosome differences (Turner syndrome, Klinefelter syndrome, and others)

Many labs also offer optional screening for microdeletions, though accuracy for these conditions is lower.

When It Is Done

NIPT can be performed starting at 10 weeks of pregnancy. Results typically come back in 5 to 10 business days.

Accuracy and Limitations

NIPT has the highest detection rate of any screening test, but it is still a screen, not a diagnosis. False positives do occur, especially for rarer conditions. A positive NIPT result should always be confirmed with diagnostic testing (amniocentesis or CVS) before any major decisions are made.

Cost

NIPT typically costs between $200 and $800 out of pocket. Many insurance plans cover it fully for those over 35 or with other risk factors. Coverage for younger patients varies. Ask your provider about your specific plan.

CVS (Chorionic Villus Sampling)

What It Is

CVS is a diagnostic procedure that collects a tiny sample of placental tissue (chorionic villi). It is done either through the cervix (transcervical) or through the abdomen (transabdominal) using ultrasound guidance.

When It Is Done

CVS is performed between 10 and 13 weeks of pregnancy, making it the earliest diagnostic option available.

What It Tells You

CVS provides a definitive chromosomal analysis with greater than 99% accuracy. It can diagnose trisomies, sex chromosome conditions, and many single-gene disorders.

Risks

The procedure-related miscarriage risk for CVS is approximately 0.5% to 1%, though this number varies by facility and provider experience. Choosing a center that performs CVS regularly can make a meaningful difference.

Amniocentesis

What It Is

Amniocentesis involves inserting a thin needle through the abdomen into the amniotic sac to withdraw a small amount of amniotic fluid. The fluid contains fetal cells that can be analyzed for chromosomal and genetic conditions.

When It Is Done

Amniocentesis is typically performed between 15 and 20 weeks of pregnancy. Results for the most common tests return within 1 to 2 weeks, though some specialized analyses take longer.

What It Tells You

Like CVS, amniocentesis is diagnostic and carries greater than 99% accuracy for chromosomal conditions. It can also test for neural tube defects and certain infections.

Risks

The procedure-related miscarriage risk for amniocentesis is approximately 0.1% to 0.3%. This makes it slightly lower-risk than CVS, though it is available later in pregnancy.

Making the Decision

There is no universally right answer about whether to pursue genetic testing, or which tests to choose. Factors that many families weigh include:

  • What would you do with the information? Some families want to know everything in advance so they can prepare. Others prefer not to test because the results would not change their plans. Both approaches are valid.
  • Your personal risk factors. Advanced maternal age, family history of genetic conditions, or a previous pregnancy with a chromosomal difference may shift the calculus.
  • Your comfort with uncertainty. Screening gives probability, not certainty. If ambiguity would cause more stress than clarity, diagnostic testing may be the better path.
  • Timing. CVS offers answers earlier, which matters to some families. Amniocentesis offers a slightly lower procedural risk.

Working with a Genetic Counselor

A genetic counselor can help you sort through these options without pressure. They are trained to present information in a balanced, non-directive way and to help you identify what matters most to you. If your provider does not automatically offer a genetic counseling referral, you can ask for one.

Finding Prenatal Care Providers on BAABY

Navigating genetic testing decisions is easier with the right support. BAABY's provider directory can help you find OB-GYNs and prenatal care specialists in your area who can walk you through your testing options and connect you with genetic counseling resources.