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Everything You Need to Know About the First Trimester Screening

Early in pregnancy, baby will be screened for potential birth defects and genetic conditions. Here’s what you can expect.
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By Dani Wolfe, Contributing Writer
Updated June 20, 2023
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As the initial excitement of being pregnant wears off (at least somewhat!), reality might be sinking in and you’re likely making a lengthy to-do checklist filled with appointments and preparations. One order of business that may be on your radar is the first trimester screening.

If you’re not familiar with the first trimester screening, not to worry. We broke down all the details, including what the test is, what it looks for, and what the results mean. Read on for everything you need to know about the first trimester screening.

What Is the First Trimester Screening?

The first trimester screening is a combination blood test and ultrasound that evaluates baby for the risk of potential birth defects and genetic conditions like Down syndrome Trisomy 21 and Trisomy 18, according to the American Pregnancy Association (APA).

It’s important to know that the first trimester screening is just that: a screening and not a diagnostic test. This means your results are only an estimate of the risk potential.

While most providers recommend this screening as part of standard prenatal care, it’s optional. Some parents-to-be seek comfort from the screening, while others may wish not to do it at all. Whatever your choice, it’s 100 percent up to you.

What Does the First Trimester Screening Include?

There are two parts to the first trimester screening: a blood test and an ultrasound evaluation, notes the APA. These two tests are usually performed at different times. The bloodwork will probably happen during or right after a routine prenatal visit, and the ultrasound will likely be during a separate appointment with an ultrasound technician.

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During the first trimester blood screening, a phlebotomist will draw blood from your arm. Aside from making sure you’ve eaten and are well hydrated, there’s nothing else you need to do to prep for it.

An ultrasound technician performs the first trimester ultrasound screening, and a maternal-fetal medicine physician, radiologist or ob-gyn reads the results. Some providers will ask you to come with a full bladder to help prop up baby for better imaging. Be sure to check the ultrasound department’s requirements before your appointment. Your provider will help you schedule this appointment, which can take up to 30 minutes, offsite if they don’t have ultrasound technicians in-house.

When Is the First Trimester Screening Performed?

Your first trimester screening is done between weeks 10 and 13, says Julie Lamppa, APRN, CNM, a certified nurse midwife at the Mayo Clinic and co-author of Obstetricks: Mayo Clinic Tips and Tricks for Pregnancy, Birth, and More.

What Does the First Trimester Screening Look For?

The first trimester screening evaluates the risk of genetic conditions like Down syndrome Trisomy 21 and Trisomy 18. According to the APA, the first trimester screening will help find about 84 percent of babies with Down syndrome and about 80 percent of babies with Trisomy 18. Here’s a peek into what each test looks for.

  • The first trimester blood screening. This test measures pregnancy-associated plasma protein-A (PAPP-A) and human chorionic gonadotropin (hCG), says Layan Alrahmani, MD, a maternal-fetal medicine specialist. Abnormal levels of either substance could signal an elevated risk for chromosomal defects.
  • The first trimester screening ultrasound. This ultrasound provides an overall look at baby and includes a nuchal translucency (NT) measurement. Nuchal translucency is the sonographic appearance of a collection of fluid under the skin behind baby’s neck. “The higher the NT, the higher the risk for Trisomy 21,” says Alrahmani. She notes that the NT measurement is only about 70 percent accurate. “The NT can also be a marker for other abnormalities, particularly heart defects. But again, accuracy isn’t very high.” This is why the timing of testing is important: Studies show that once your pregnancy reaches 14 weeks, the base of baby’s neck becomes less transparent, and is no longer a reliable method of testing.

Your provider will combine the hCG and PAPP-A blood test results, the ultrasound findings and mom’s demographic information to calculate a risk ratio. Parents-to-be usually receive their first trimester screening results within a week or two after both tests are completed, according to Nemours KidsHealth.

First Trimester Screening vs NIPT

The first trimester screening and noninvasive prenatal testing (NIPT) are similar in that they both look for genetic abnormalities in baby. But while the first trimester screening uses a bloodwork-ultrasound combo, the NIPT only uses blood test results.

The NIPT is a newer screening option that looks for free fragments of DNA in the bloodstream, notes John Hopkins Medicine. Research suggests that NIPT is generally more accurate than the first trimester screening at detecting abnormalities. The DNA picked up provides clues to the risk of baby having various genetic conditions. According to Cleveland Clinic, NIPT can also assess risk for Turner syndrome, Klinefelter syndrome and triple X syndrome, and it’s very accurate at determining baby’s sex.

Both the first trimester screening and NIPT are optional. Parents-to-be can choose one or the other, both or none. The first trimester screening is typically recommended to every expecting person, but the NIPT is usually not offered as the first method of testing. If the first trimester screening results are abnormal—or another test turns up a potential red flag–it’s a common next step. “It can be performed any time after 10 weeks gestation," notes Lamppa. “If any concerns are noted on the anatomy ultrasound, routinely done between 18 to 22 weeks, you could elect for NIPT at this time for further information gathering.”

What Do Results of the First Trimester Screening Mean?

Again, it’s important to remember that the first trimester screening isn’t a diagnostic test—it’s only a screening that measures the potential risk of certain genetic conditions. “Screening tests aren’t as accurate as diagnostic tests, but we often start with them because they aren’t invasive,” says Alrahmani.

Your test results will typically come back as either “normal” or “abnormal,” and you’ll be given a risk ratio for each condition.

First trimester screening results in the normal range mean there’s a low chance baby has a birth defect or genetic abnormality. According to Alberta Health Services, if your ratio comes back as 1 out of 300, this means your results are normal.

An abnormal first trimester screening result means there’s a higher-than-average chance that baby has a chromosomal abnormality. Per Alberta Health Services, doctors often use a specific number as a cutoff for an abnormal result. For example, your doctor might have a cutoff ratio such as 1 out of 200. This means that if your result is 1 out of 200 or 1 out of any number less than 200, you have an abnormal result.

Keep in mind that your results aren’t 100 percent accurate. Since due dates are usually estimates, it’s possible, for example, that your test was done too early or too late, resulting in inaccurate findings.

Next Steps After the First Trimester Screening

If your first trimester screening results are normal, you’ll most likely carry on with regular prenatal care and continue other screenings and tests as your doctor recommends. If your results come back abnormal, your doctor will usually offer some next steps.

“It’s recommended that someone with abnormal genetic screening results would get a diagnostic test—chorionic villus sampling or amniocentesis, depending on gestational age,” notes Alrahmani. You can also turn to the NIPT. Or, you can opt out of testing altogether if you wish.

Try to stay calm, and remember that these aren’t definitive results. And always make sure to talk out your options with your provider to decide what’s best for you.

Please note: The Bump and the materials and information it contains are not intended to, and do not constitute, medical or other health advice or diagnosis and should not be used as such. You should always consult with a qualified physician or health professional about your specific circumstances.

Sources

Layan Alrahmani, MD, FACOG, is a board-certified physician in maternal-fetal medicine, obstetrics and gynecology and lifestyle medicine. She received her medical degree from the University of Jordan and currently practices in the Chicago area.

Julie Lamppa, APRN, CNM, is a certified nurse midwife at the Mayo Clinic in Rochester, Minnesota, and the co-author of Obstetricks: Mayo Clinic Tips and Tricks for Pregnancy, Birth, and More.

American Pregnancy Association, First Trimester Screening

Diagnostics, A Pain in the Neck: Lessons Learnt from Genetic Testing in Fetuses Detected with Nuchal Fluid Collections, Increased Nuchal Translucency versus Cystic Hygroma—Systematic Review of the Literature, Meta-Analysis and Case Series, December 2022

Nemours KidsHealth, Prenatal Test: First Trimester Screening, August 2018

Johns Hopkins Medicine, First Trimester Screening, Nuchal Translucency and NIPT

Singapore Medical Journal, Combined First Trimester Screen or Noninvasive Prenatal Testing or Both, January 2015

Cleveland Clinic, NIPT Test, October 2022

Alberta Health Services, First-Trimester Screening for Birth Defects, February 2023

Learn how we ensure the accuracy of our content through our editorial and medical review process.

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