Medically reviewed by Dr. Ruqaiya Khan, MD, FACOG.
Prenatal screening tests help estimate the likelihood of certain chromosomal conditions and birth defects during pregnancy. This guide walks through the major prenatal screening tests, when they’re offered, and what the results actually mean.
What are prenatal screening tests?
Prenatal screening tests are non-invasive tests – blood draws and ultrasounds – that estimate the probability of conditions like Down syndrome (trisomy 21), trisomy 18, and neural tube defects. Screening tests don’t diagnose a condition; they identify pregnancies that may benefit from further diagnostic testing, per ACOG guidance.
First-trimester screening (weeks 11-13)
Nuchal translucency (NT) ultrasound
This ultrasound measures the fluid at the back of the baby’s neck. An increased measurement can be associated with a higher chance of chromosomal conditions or heart defects.
First-trimester blood screen
A blood draw measures two proteins, PAPP-A and hCG. Combined with the NT measurement and your age, this produces a risk estimate for trisomy 21 and trisomy 18.
Cell-free DNA screening (NIPT)
Non-invasive prenatal testing (NIPT) analyzes small fragments of placental DNA circulating in your blood, starting as early as 9-10 weeks. NIPT is highly accurate for detecting trisomy 21, 18, and 13, and can also screen for sex chromosome differences and reveal fetal sex. It’s a screening test, not diagnostic, so a high-risk result is typically followed up with diagnostic testing.
Second-trimester screening (weeks 15-20)
Quad screen
A blood test measuring four substances – AFP, hCG, estriol, and inhibin-A – used to assess risk for trisomy 21, trisomy 18, and neural tube defects like spina bifida. It’s often used for people who missed first-trimester screening or want additional information.
Anatomy ultrasound (18-22 weeks)
A detailed ultrasound examining your baby’s organs, growth, and structural development. While primarily an anatomical survey, it can also flag “soft markers” that may prompt further discussion.
Diagnostic testing: CVS and amniocentesis
Unlike screening tests, chorionic villus sampling (CVS, around weeks 10-13) and amniocentesis (around weeks 15-20) analyze fetal cells directly and can diagnose chromosomal conditions with high accuracy. These are invasive procedures carrying a small miscarriage risk, and are usually offered after a higher-risk screening result or based on personal or family history.
Understanding your prenatal screening results
A screening result is expressed as a risk estimate (for example, “1 in 500”), not a yes-or-no answer. A “screen positive” result means your risk is higher than the cutoff used – it does not mean your baby has the condition. Many people with a screen-positive result go on to have diagnostic testing that comes back normal. A genetic counselor can help interpret results and discuss next steps.
Do I have to get prenatal screening tests?
Prenatal screening is entirely optional. Some people want as much information as possible to prepare; others prefer not to test unless there’s a specific concern. There’s no right answer – discuss your preferences and any family or personal history with your provider so you can make the choice that’s right for you.
Quick comparison of prenatal screening tests
- NT ultrasound + first-trimester blood screen: Weeks 11-13, screening only
- NIPT (cell-free DNA): From ~9-10 weeks, screening only, highly accurate
- Quad screen: Weeks 15-20, screening only
- Anatomy ultrasound: Weeks 18-22, structural survey
- CVS: Weeks 10-13, diagnostic
- Amniocentesis: Weeks 15-20, diagnostic
Estimate your own testing windows with the gestational age calculator or due date calculator.
FAQs about prenatal screening tests
Are prenatal screening tests accurate?
Prenatal screening tests, especially NIPT, have high detection rates for the conditions they target, but they are still screening tools, not diagnostic tests. A positive screening result should be confirmed with diagnostic testing like CVS or amniocentesis.
Do prenatal screening tests carry any risk?
Standard prenatal screening tests (blood draws and ultrasounds) carry no risk to you or your baby, unlike diagnostic tests such as CVS and amniocentesis, which carry a small miscarriage risk.
When should I schedule prenatal screening tests?
Most prenatal screening tests are offered in specific windows: first-trimester screening at weeks 11-13, NIPT from about week 9-10, and second-trimester quad screen at weeks 15-20. Talk to your provider early to plan your testing schedule.
Does insurance cover prenatal screening tests?
Coverage for prenatal screening tests varies by insurance plan and personal risk factors. Check with your insurance provider and your OB-GYN’s office about costs before testing.
Related Resources
- First Trimester Guide (Weeks 1–13)
- Second Trimester Guide (Weeks 14–27)
- Due Date Calculator
- Fetal Weight Percentile Calculator
This page is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your OB-GYN, midwife, or a genetic counselor about which tests are right for you.