first trimester screening

Your Guide to First-Trimester Screening, Tests, and Bloodwork

By Carol Caffin
Reviewed by Elizabeth Eden, M.D.
June 10, 2024

The first trimester of your pregnancy can feel like a never-ending series of blood draws, urine tests, and ultrasounds. You might wonder, Why so many, and what are they all for?

Most of the tests and screenings performed early in pregnancy are meant to check that all is well with both you and your baby, to advise you of potential health risks, and to gauge risk of genetic and other abnormalities.

“First-trimester tests include both the routine tests done at the initial exam as well as screening for chromosomal defects, such as Down syndrome and neural tube defects,” says Natalie A. Bowersox, M.D., board-certified ob-gyn, residency director, and vice chair of obstetrics and gynecology at Cleveland Clinic Akron General.

Especially if this is your first pregnancy, it’s understandable if you feel nervous or anxious about your health and that of your baby. But knowing how and why specific prenatal tests are done may help put your mind at ease. It’s also a good idea to learn the testing lingo.

Here’s what we’ll cover in this article:

Routine Screenings and Tests

  • Pap Smear
  • Prenatal Blood Panel
  • Urine Tests

Optional Screenings and Tests

  • Nuchal Translucency Screening
  • Maternal Serum Test
  • Noninvasive Prenatal Screenings

Prenatal Diagnostic Testing

  • Chorionic Villus Sampling
  • Genetic Carrier Screening

First Trimester Prenatal Screening vs. Diagnostic Tests

“There is a difference between screening and diagnostic tests,” says board-certified genetic counselor Michele Branch, of Crystal Run Healthcare in Middletown, New York.

“Screening tests such as ultrasounds and blood tests cannot tell with certainty if a fetus is affected with a chromosomal condition. Instead, they tell us if there is an increased or decreased risk.”

In other words, the results of a prenatal screening test in your first trimester won’t tell you whether there is or isn’t a problem—but the results may help you decide whether or not you want to pursue further testing.

On the other hand, prenatal diagnostic tests are meant to identify certainties or near certainties, rather than possibilities or risks. These tests can diagnose some conditions with close to 100% accuracy. However, a few of the diagnostic tests themselves carry risks. Your doctor will discuss the benefits and risks of these tests with you.

Routine First-Trimester Tests and Screenings

Here are some of the most common first-trimester screenings and what you need to know about them.

First-Trimester Pap Smear Test

At your first prenatal visit, you’ll likely be given a full pelvic exam and a Pap smear. This test is used to look for changes in cervical cells that could indicate cervical cancer or conditions that can develop into cancer.

Pap smears, when performed with HPV testing (usually done using the same swab), can detect up to 95% of precancerous cervical changes. These, if caught early, are highly curable.

What Happens During a Pap Smear: Your ob-gyn will use a speculum to hold the walls of your vagina wider in order to examine both the vagina and the cervix before collecting some cells from the cervix with a soft brush and spatula. The collected cells will be sent to a lab to check for abnormalities.

When Is the Pap Smear Done? First prenatal visit

How to Prepare for a Pap Smear: For 48 hours before a prenatal pap smear, avoid vaginal intercourse, and don’t insert anything into the vagina.

Next Steps: If you have abnormal pap smear results, your doctor will discuss with you the nature of the abnormality and tell you whether further tests are needed, whether they can be done safely during pregnancy, or whether they can wait until after your baby is born.

Your doctor may recommend a diagnostic procedure called colposcopy to determine whether you have cervical dysplasia (precancerous cervical change). A cervical biopsy is a more definitive test but should be reserved for only extremely suspicious areas and deferred, in most cases, until six weeks after childbirth.

First-Trimester Pregnancy Blood Test

At your first prenatal visit, you’ll also be given initial pregnancy blood tests, often collectively called a “prenatal panel.”

This includes:

  • A complete blood count (CBC), which measures several components of your blood and checks for signs of anemia, low or high platelet count (which can be caused by a variety of disorders), leukemia, and other disorders, as well as infection
  • Blood typing, including an Rh screen (whether blood is Rh negative or Rh positive)
  • Rubella viral antigen screen
  • Screening for HIV, sexually transmitted diseases (STDs), hepatitis, clotting disorders, cystic fibrosis, and more

Other first-trimester blood tests and screenings may be done based on individual risk factors.

What Happens During a Prenatal Blood Panel: Blood is drawn from a vein in your arm and collected in tubes.

When Is the Prenatal Blood Panel Done? First prenatal visit

How to Prepare for Your Prenatal Blood Panel: No preparation is needed for the prenatal panel blood test.

Next Steps: If the blood tests detect any diseases or signs of them, your doctor may recommend medication or further testing.

Urine Tests

Urine tests are taken throughout your pregnancy. Your doctor may do a urinalysis, a urine culture, or both.

  • A urinalysis is used to screen for urinary tract infections (UTIs), kidney disease, preeclampsia (high blood pressure), diabetes, and other red flags.
  • A urine culture tests for bacteria in the urine, which can indicate a UTI.

What Happens During a Prenatal Urine Test: You’ll be asked to collect a “clean catch” urine sample (meaning you catch it midstream) in a sterilized cup. The urine will then be tested with a chemically treated strip and may also be sent to a lab.

When Are Urine Tests Done in Pregnancy? First prenatal visit and all or most other prenatal visits

How to Prepare for a Urine Test: You may want to drink water before the test so that you can pee more easily.

Next Steps: If your urine shows signs of a problem, your doctor will discuss with you whether treatment, medication, or further testing is needed.

Optional First-Trimester Screenings and Tests

“Genetic screening should be offered to all patients,” says Raquel Dardik M.D., a board-certified ob-gyn and associate professor at NYU Langone in West Palm Beach, Florida.

“The provider should discuss what the test can and cannot do, and what the options are based on the results. Some patients may opt not to have these tests done.”

Your first-trimester screenings can also include the following tests:

  • Nuchal Translucency Screening
  • Maternal Serum Test
  • Noninvasive Prenatal Testing

Nuchal Translucency Screening

A nuchal translucency (NT) screening is an ultrasound exam that measures the fluid-filled space at the back of your baby’s neck. An increased nuchal translucency may be associated with a risk of certain chromosomal abnormalities.

“An abnormal measurement means there may be an increased risk that the baby has Down syndrome (trisomy 21),” says Bowersox, “or a defect of the heart, skeleton, abdominal wall, or another type of abnormality.”

What Happens During a Nuchal Translucency Test: The measurements are taken during an ultrasound. This is done in combination with a maternal serum (blood) test.

When Is Nuchal Translucency Typically Done: 10–13 weeks

How to Prepare for an NT Test: No preparation needed

Next Steps: You’ll also need to have your blood drawn.

Maternal Serum (Blood) Test

The other optional screening—a maternal serum (blood) test—measures two substances in your blood:

  • Pregnancy-associated plasma protein-A (PAPP-A), a protein made by the placenta
  • Human chorionic gonadotropin (HCG), a hormone made by the placenta

Abnormal levels of these substances may indicate an increased risk for chromosomal defects.

What Happens During a Maternal Serum Screening: The blood is drawn and analyzed.

When Is Maternal Serum Screening Done? 10–13 weeks

How to Prepare for a Maternal Serum Screening: No preparation needed

Next Steps: If the results of the combination of ultrasound and blood screenings show an increased risk of chromosomal abnormalities, your doctor will talk to you about your options and may recommend a diagnostic test: either chorionic villus sampling (CVS) or amniocentesis (usually done around 16 weeks).

Noninvasive Prenatal Testing (NIPT)

A Noninvasive Prenatal Test (NIPT) is also known as cell-free DNA (or cfDNA) screening.

“This test takes a sample of blood from the pregnant patient that measures fetal DNA released from the placenta,” Bowersox says.

NIPT screens for the common chromosomal disorders:

It also screens for sex chromosome disorders such as Turner syndrome and Klinefelter syndrome. If you want to know your baby’s sex, NIPT can tell you that, too.

Noninvasive prenatal testing can also reveal whether your baby is Rh positive or negative.

Rh factor is a protein that can be found on the red blood cells of the majority of people. If you’re Rh negative, and your fetus is Rh positive, you’ll need an injection of a medication called RhoGAM. This shot is given before the birth to prevent issues related to Rh incompatibility.

As of 2020, the American College of Obstetricians and Gynecologists (ACOG), which had previously recommended this screening only for pregnant people 35 and older or for those with other known risk factors, now recommends NIPT for all pregnant people.

What Happens During a Noninvasive Prenatal Test: Your blood is drawn and tested.

When Is a Noninvasive Prenatal Test Done? 9–10 weeks

How to Prepare for a Noninvasive Prenatal Test: No preparation needed

Next Steps: If the NIPT suggests that there could be a higher risk of a chromosomal disorder, your doctor will talk to you about your options and may recommend chorionic villus sampling.

First-Trimester Diagnostic Testing

“The decision to proceed with diagnostic testing is a personal one,” Branch says, “and should be made by each patient or couple after discussing the information and risks with their provider or genetic counselor.”

Chorionic Villus Sampling (CVS)

While NIPT and NT screening assess risks for chromosome abnormalities and disorders, CVS is used to diagnose them. If an NIPT or NT indicates a higher risk for chromosomal disorders, your doctor may recommend a CVS.

“This involves inserting a needle through the abdomen and taking a small sample of placental tissue to analyze,” Branch says.

What is Chorionic Villus Sampling?

Unlike NIPT, NT, and other screens, which carry no risk to you or your baby, CVS carries a very small chance of miscarriage. Branch notes that “the risk for miscarriage with a CVS procedure is 1% or less.”

Other risks of a Chorionic Villus Sampling procedure include

  • Cramping
  • Bleeding
  • Leaking of amniotic fluid
  • Infection
  • Preterm labor
  • Limb defects in the baby, if performed before 9 weeks (rarely)

How a Chorionic Villus Sampling Is Done: There are two types of CVS procedures:

  • Transabdominal. In this procedure, a needle is inserted through the abdomen and uterus to the placenta.
  • Transcervical. In this type of CVS, a catheter is inserted through the cervix to the placenta. If you’re pregnant with twins or other multiples, you’ll need to have a CVS from each placenta.

When Is Chorionic Villus Sampling Done? 10–12 weeks

How to Prepare for a CVS Test: No preparation needed

Next steps: If you get a positive result, ACOG recommends seeing a specialist for genetic counseling and having an ultrasound evaluation to confirm results.

Genetic Carrier Screening

Genetic carrier screening is an optional screen that can be done to see what, if any, conditions are carried by you and your baby’s other genetic parent during the first trimester.

If you both carry the same genetic condition, you may have an increased risk of having a baby with that condition.

What Diseases Can Be Detected Through Genetic Testing: Some of the more common conditions that are screened for are:

  • Cystic fibrosis
  • Sickle cell anemia
  • Tay-Sachs disease
  • Thalassemia

What Happens During Genetic Testing: A sample of blood or saliva is taken, or tissue is swabbed from the inside of your cheek.

When Is Genetic Carrier Screening Done? Ideally before pregnancy, but if during pregnancy, the earlier the better

How to Prepare for Genetic Carrier Screening: No preparation needed

Next Steps: Depending on the results, it may be suggested that you consult with a doctor and/or a genetic counselor to discuss potential risks and testing options.

Should You Opt for Screenings and/or Tests for Genetic Abnormalities?

“Do your homework and really think about what you would do with the results,” Bowersox says. “Would a positive result alter whether you would continue the pregnancy? If so, it’s a good test to consider.”

There are other reasons to consider genetic testing, too.

Knowing your child might have a medical condition can help you prepare to have medical specialists ready to assess and possibly treat them soon after their birth to improve the outcome.

You may also want to put support systems in place before you deliver, and/or inform other family members of a child’s potential special needs.

The decision is entirely up to you (or up to you and your baby’s other genetic parent), but you should also feel free to talk everything out with your doctor.

Understanding the Importance of First-Trimester Testing

The list of first-trimester screening and tests may seem long and overwhelming, but your doctor will help you keep track. That’s one reason it’s important to attend regular prenatal visits.

Routine screenings during pregnancy help your doctor understand your health and that of your growing baby. If you have concerns or just want peace of mind, you may choose to have optional screenings. Based on the screening results, you may opt for diagnostic testing.

Any time you have questions about prenatal screening and testing, talk to your doctor. You may also make an appointment with a genetic counselor to make the right genetic testing decisions for you and your baby.

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