The first trimester screening (or first trimester screen) typically includes a maternal blood screening test and an ultrasound exam.
It's done to see if a fetus is at risk of having a chromosomal abnormality (such as Down syndrome or Edward syndrome) or birth defect (such as heart problems).
It's important to remember that this is a screening test, not a diagnostic test. If the test shows there might be a problem, another test must be done to confirm or rule out a diagnosis.
The screen is considered safe, but it's your decision whether or not to have it. The benefit of screening in the first trimester is more time for parents to prepare for or address any health problems their baby may have.
When getting any screening, remember that there's a chance of false-positive or false-negative results:
Talk to your doctor if you have questions about these screenings or your results.
This screening test ideally is done in two parts — a blood sample and an ultrasound exam:
Women whose results show a high risk for carrying a baby with a chromosomal abnormality are offered diagnostic testing, usually through chorionic villus sampling (CVS) in the first trimester or amniocentesis in the second trimester.
Those who are not shown to be high risk in the first trimester are still offered a second trimester screening. That screening, which consists of more blood tests, checks for chromosomal abnormalities and neural tube defects, and helps to confirm the findings from the first trimester screen.
The blood screening is usually done between 9 and 14 weeks. Women who also get an ultrasound have one between 11 and 14 weeks.
Blood screening results usually are ready within a week or two. Ultrasound results can be immediate.
When both the blood test and ultrasound are done, doctors usually calculate the results together. This is called a combined first trimester screening.
Not all doctors calculate a woman's risk this way. Some wait until after a woman has had other screenings in the second trimester. This is called an integrated screening. Other practitioners don't do first trimester ultrasounds, instead determining a woman's risk using the results of her first trimester and second trimester blood screenings. This is called a serum integrated screening.
How your doctor calculates your results depends on your age, health risks, and the services available at the provider's office.
Reviewed by: Armando Fuentes, MD
Date Reviewed: Aug 2, 2018