Screening and diagnostic tests
MedlinePlus says a screening test estimates risk, and an abnormal result means more information is needed, while a diagnostic test confirms whether a condition is present.[1]
ACOG says both screening and diagnostic testing are offered to all pregnant women.[2] It says there is no right or wrong answer about testing.[2]
First-trimester screening
ACOG says first-trimester screening is a blood test plus an ultrasound measurement called nuchal translucency.[2]
Sources differ
The NHS says its dating scan may include a nuchal translucency measurement as part of Down syndrome screening.[4]
Cell-free DNA screening (NIPT)
ACOG says cell-free DNA screening can be done from 10 weeks, with results in about 1 week.[2]
It says the test screens for Down syndrome, trisomy 13, trisomy 18 and problems with the number of sex chromosomes.[2]
ACOG says a positive cell-free DNA result should be followed by a diagnostic test, amniocentesis or chorionic villus sampling.[2]
MedlinePlus also lists cell-free DNA screening among prenatal tests.[5]
What results mean
ACOG explains screening results this way:[2]
- a positive screen means a higher chance, not a diagnosis;[2]
- a negative screen means a lower chance, but does not rule a condition out;[2]
- false positive and false negative results can happen.[2]
NICHD suggests considering genetic counseling when you review your family history.[6] ACOG says carrier screening, with a blood test or cheek swab, can be done before or during pregnancy.[2]
NIPT vs first trimester screening at a glance
| First-trimester screening | Cell-free DNA screening (NIPT) | |
|---|---|---|
| What it is | A blood test plus an ultrasound measurement called nuchal translucency[2] | A blood test that screens cell-free DNA[2] |
| When | Usually 10 to 13 weeks (ACOG);[2] weeks 11 to 14 (OWH)[3] | From 10 weeks, with results in about 1 week[2] |
| Screens for | Down syndrome and some other chromosome conditions; ask your provider which | Down syndrome, trisomy 13, trisomy 18 and problems with the number of sex chromosomes[2] |
| A positive result means | A higher chance, not a diagnosis[2] | A higher chance; ACOG says to follow up with a diagnostic test, amniocentesis or CVS[2] |
Both are screening tests, and both are optional.[1] Your provider can explain which one fits your pregnancy and what each result would mean for you.
Questions families ask
When can NIPT be done?
ACOG says cell-free DNA screening can be done from 10 weeks.[2]
Does a positive screen mean the baby has a condition?
ACOG says a positive screen means a higher chance, not a diagnosis.[2]
Do I have to have these tests?
MedlinePlus says prenatal testing is optional and is your decision, made with your provider.[1]
What is the difference between NIPT and first trimester screening?
First-trimester screening combines a blood test with a nuchal translucency ultrasound.[2] NIPT, or cell-free DNA screening, is a blood test that can be done from 10 weeks.[2] Both are screening tests, not diagnoses.
What does a negative NIPT result mean?
ACOG says a negative screen means a lower chance, but it does not rule a condition out.[2]
What happens after a positive NIPT?
ACOG says a positive cell-free DNA result should be followed by a diagnostic test, amniocentesis or chorionic villus sampling.[2]
Free from UpOnly Learning. Written for families of every faith. No outside ads and no affiliate links. Every fact on this page comes from the sources listed below. How we source and review these pages
Updated 2026-10-24: first published.
Sources
All sources were opened and checked on the date shown.
- MedlinePlus (National Library of Medicine). Prenatal Testing. Checked October 24, 2026.
- American College of Obstetricians and Gynecologists. Prenatal Genetic Screening Tests. Checked October 24, 2026.
- Office on Women's Health (HHS). Prenatal care and tests. Checked October 24, 2026.
- NHS (United Kingdom). 11 weeks pregnant guide. Checked October 24, 2026.
- MedlinePlus (National Library of Medicine). Prenatal care in your second trimester. Checked October 24, 2026.
- Eunice Kennedy Shriver National Institute of Child Health and Human Development (NIH). Can you promote a healthy pregnancy before getting pregnant?. Checked October 24, 2026.