First Trimester Tests: What to Know

The first trimester runs from the start of your pregnancy through the end of week 13. It's usually when you have your first prenatal visits, along with tests you'll likely have and others you can choose to have done.

This guide walks through each test: what it checks for, when it happens, and what the results can and can't tell you. Some tests are routine for everyone, but genetic screening is always your choice.

Which first trimester tests are routine and which are optional?

• Routine for everyone: a pregnancy test, first visit blood work, a urine test, STI tests and a dating ultrasound
• Optional: carrier screening, cell-free DNA screening (NIPT), the first trimester screen and chorionic villus sampling (CVS)

Screening tests vs. diagnostic tests

Screening tests estimate the chance of a condition. They're low-risk, usually a blood draw or an ultrasound, but they can't give you a definite answer. A "high-chance" result means more testing may be offered, not that your baby has a condition. A "low-chance" result is reassuring, but it doesn't rule a condition out completely.

Diagnostic tests give a more definite answer. Some, like CVS, carry a small risk of miscarriage.

Tests to confirm pregnancy and at your first visit

Pregnancy test (hCG)

When: From about the time of a missed period

A pregnancy test looks for human chorionic gonadotropin (hCG), a hormone your body starts making soon after a fertilized egg implants in your uterus. Home tests check your urine. Your provider may also order a blood test, which can measure the exact amount of hCG.

First visit blood work

When: At your first prenatal visit, often between 8 and 12 weeks

At your first visit, you'll usually have a set of blood tests, sometimes called a prenatal panel. These tests check:

• Blood type and Rh factor, and whether you have certain antibodies
• Blood count, to look for anemia
• Rubella immunity, to see if you're protected
• Hepatitis B and hepatitis C
• HIV and syphilis

Depending on your health history, your provider may also check your blood sugar or thyroid.

Good to know: The CDC recommends hepatitis C testing during every pregnancy. Many infections can be treated or managed during pregnancy, which helps protect both you and your baby. If you're Rh-negative, you'll likely be offered a shot called Rh immune globulin later in pregnancy and after certain events, like bleeding.

Urine test

When: At your first visit, then at many visits after

A urine sample can check for a urinary tract infection, along with protein and sugar.

Good to know: Bladder infections are treated during pregnancy even if you don't have symptoms. Left untreated, they can lead to a kidney infection.

STI tests and Pap test

When: Usually at your first visit

You'll likely be tested for chlamydia and gonorrhea, depending on your age and risk. If you're due for a Pap test to check for cervical cell changes, it may be done at this visit too.

Good to know: These tests are quick and routine, and most infections are easily treated.

First trimester ultrasounds

Dating ultrasound

When: Usually 6–13 weeks

Your first ultrasound is often done early in the first trimester. Because your baby is so small, it may be a transvaginal ultrasound, which gets a clearer picture by looking from inside the vagina, closer to your uterus. Your provider or a sonographer gently places a slim, lubricated wand with a protective cover a few inches into your vagina. It usually takes a few minutes and may feel like pressure, but it shouldn't hurt. You'll be asked to empty your bladder first, and you can ask to insert the wand yourself or to have someone with you.

What it checks for: Your due date, your baby's heartbeat and how many babies you're carrying.

Good to know: A first trimester ultrasound is the most accurate way to set your due date. That date guides the timing of other tests later in pregnancy, so it's worth getting right.

First trimester screen (nuchal translucency) — optional

When: Usually 11–14 weeks (the blood draw can start at 10 weeks)

The first trimester screen combines an ultrasound with a blood test. The ultrasound measures the fluid at the back of your baby's neck, called the nuchal translucency (NT). The blood test measures two substances, PAPP-A and hCG.

What it checks for: The chance of Down syndrome, trisomy 18 and trisomy 13.

Good to know: This is a screening test, not a diagnosis. Many practices now offer cell-free DNA screening instead of, or along with, this screen. Even if you choose cell-free DNA, an NT ultrasound can still spot some physical differences that a blood test can't.

Genetic screening and testing

Every test in this section is optional. Your provider should offer them, but you decide whether to have any of them done.

Carrier screening — optional

When: Ideally before pregnancy, or at your first prenatal visit

Carrier screening is a blood or saliva test that checks whether you carry a gene for certain inherited conditions. A carrier usually doesn't have the condition but could pass the gene on to a baby.

What it checks for: ACOG recommends offering everyone screening for cystic fibrosis, spinal muscular atrophy, and blood conditions like sickle cell disease and thalassemia. Larger panels that check for many more conditions are also available.

Good to know: Most carriers are healthy and have no family history of the condition. If you're a carrier, your partner may be offered testing to understand the chance your baby could be affected.

Cell-free DNA screening (NIPT) — optional

When: Any time from 10 weeks

Cell-free DNA screening, also called noninvasive prenatal testing (NIPT), is a blood test. It looks at small pieces of DNA from the placenta that circulate in your bloodstream.

What it checks for: The chance of Down syndrome and other chromosome conditions. It can also show your baby's sex, so let your provider know if you'd rather not find out.

Good to know: Cell-free DNA is the most accurate screening test for Down syndrome, but it's still a screen, not a diagnosis. Sometimes the lab can't get a clear result, called a "no-call." You may be offered a repeat blood draw or other testing. A no-call isn't the same as a high-chance result.

Chorionic villus sampling (CVS) — optional

When: Usually 10–13 weeks

CVS is a diagnostic test that takes a small sample of tissue from the placenta. It's done either through your cervix or through your belly, using ultrasound for guidance.

What it checks for: Chromosome conditions and some genetic conditions.

Good to know: CVS can give a more definite answer earlier than amniocentesis, which is done in the second trimester. Because it carries a small risk of miscarriage, it's usually offered after a high-chance screening result, a family history or a positive carrier screen. Anyone can choose diagnostic testing, though, with or without screening first.

Questions to ask before any prenatal test

You deserve to understand why a test is being offered and what it can tell you. Before you say yes or no, you can ask:

• Is this a screening test or a diagnostic test?
• What will the results tell us, and what won't they?
• What are the risks?
• When and how will I get my results?
• What happens if the result is abnormal?
• Would the results change my care or my baby's care?
• Is it covered by my insurance?

If you're deciding about genetic testing, you can ask to talk with a genetic counselor first. You might say:

"Before I decide on genetic screening, can I talk with a genetic counselor?"

The BirthX takeaway

The first trimester can feel like a whirlwind of appointments and lab slips. Some tests are routine parts of care for everyone. Others, especially genetic screening, are entirely your choice.

Knowing what each test is for, and what it can and can't tell you, helps you make informed decisions from the very start of your pregnancy. Download the one-page summary to bring to your next appointment, and ask every question you have. You deserve clear answers and care that respects your choices.

This article is for education only and is not a substitute for medical advice. Always talk with your provider about which tests are right for you.

Sources: MedlinePlus, Prenatal panel; Children's Hospital of Philadelphia, First trimester screening; CDC, Test for hepatitis C during every pregnancy; ACOG, Screening for fetal chromosomal abnormalities (Practice Bulletin No. 226); Quest Diagnostics, The evolution of carrier screening: understanding current recommendations.