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Maternity

Prenatal Testing Guide: Screenings, Scans and What to Expect (2026)

EasyTot · May 15, 2026

Prenatal testing can feel overwhelming — there are screenings, diagnostic tests, ultrasounds and blood draws at seemingly every appointment. Knowing what each test looks for, when it happens and what kind of answer it can give makes the decisions easier and the waiting less anxious.

Short answer: prenatal tests fall into two groups. Screening tests (blood work and ultrasound) tell you the chance of a condition; diagnostic tests (CVS and amniocentesis) tell you whether it is actually present. The American College of Obstetricians and Gynecologists (ACOG) says both kinds are offered to everyone who is pregnant, and that it is your choice whether to have them.

Key distinction: Screening tests tell you the probability of a condition. Diagnostic tests confirm whether a condition exists. A screening result is never a diagnosis — in either direction.

Prenatal Testing Timeline: Week by Week

Every timing below is the one ACOG publishes for patients; your own provider may shift a test earlier or later for your situation.

When	Test	Type	What it looks for
Early pregnancy	Complete blood count, blood type and Rh factor, urinalysis, urine culture, infection tests	Routine	Anemia, Rh status, urinary tract infection, rubella, hepatitis B and C, HIV and other STIs
10–13 weeks	First-trimester screening (blood test + nuchal translucency ultrasound)	Screening	Chance of Down syndrome or another aneuploidy
From 10 weeks	Cell-free DNA testing (NIPT)	Screening	Chance of Down syndrome, trisomy 13, trisomy 18, sex-chromosome differences
10–13 weeks	Chorionic villus sampling (CVS)	Diagnostic	Chromosomal and certain genetic conditions
15–20 weeks	Amniocentesis	Diagnostic	Chromosomal and certain genetic conditions
15–22 weeks	Quad blood test	Screening	Chance of Down syndrome, trisomy 18, neural tube defects
18–22 weeks	Standard ultrasound exam	Screening	Major physical differences in the brain and spine, face, abdomen, heart and limbs
24–28 weeks	Glucose screening	Screening	Gestational diabetes
36–38 weeks	Group B strep culture	Routine	GBS bacteria that could pass to the baby in labor

A pregnancy journal with a page per appointment is the simplest way to keep this straight: write the test, the date, the questions you want to ask, and the result when it comes back.

Screening vs. Diagnostic Tests

Screening tests assess the chance of certain conditions using a blood sample, an ultrasound, or both. They carry no risk to the pregnancy, but they cannot give a definite answer. ACOG's guide to prenatal genetic screening explains that a positive result means a higher chance than in the general population, and a negative result means a lower chance — it "does not rule out the possibility" of the condition. ACOG also notes that any test can produce false positives and false negatives, and that your health care professional can give you those rates for each test.

Diagnostic tests — amniocentesis and chorionic villus sampling (CVS) — analyze cells from the amniotic fluid or the placenta and give a more definite result. They are invasive: ACOG's guide to diagnostic tests says there is "a very small chance of pregnancy loss" with amniocentesis, and that the chance of miscarriage with CVS is slightly higher than with amniocentesis. ACOG says diagnostic testing is an option for everyone, not only after a positive screen.

First Trimester Testing

Initial Blood Work (First Prenatal Visit)

ACOG's list of routine tests early in pregnancy includes a complete blood count (which can show anemia), blood type and Rh factor, a urinalysis and a urine culture, plus tests for rubella, hepatitis B and hepatitis C, HIV, other sexually transmitted infections and, for some people, tuberculosis. ACOG says you should be tested for syphilis three times: at the first prenatal visit, in the third trimester and at delivery. Our first trimester guide covers what else happens at that first appointment.

NIPT (Cell-Free DNA Testing)

Cell-free DNA is the small amount of DNA released from the placenta into your bloodstream. A sample of your blood can be screened for Down syndrome (trisomy 21), trisomy 13, trisomy 18 and differences in the number of sex chromosomes — which is also why this test can reveal the baby's sex if you want to know. ACOG says it can be done starting at 10 weeks, that results take about a week, and that a positive result "should be followed by a diagnostic test with amniocentesis or CVS."

First-Trimester Screening and the NT Scan

Between 10 and 13 weeks, a blood test that measures two substances is paired with a nuchal translucency (NT) ultrasound, which measures the thickness of a space at the back of the baby's neck. ACOG explains that an abnormal measurement means an increased chance of Down syndrome or another aneuploidy, and that it is also linked to physical differences of the heart, abdominal wall and skeleton.

This is also the trimester when a daily prenatal vitamin matters most; our prenatal vitamins guide explains what to look for on the label.

Second Trimester Testing

Anatomy Scan (18–22 Weeks)

This is the detailed ultrasound most parents look forward to. ACOG's ultrasound guidance says you should have at least one standard exam during pregnancy, usually at 18 to 22 weeks; it checks for major physical differences in the brain and spine, facial features, abdomen, heart and limbs. It is often when you can learn the baby's sex if cell-free DNA testing has not already told you. The second trimester guide covers the rest of these weeks.

Quad Screen (15–22 Weeks)

The "quad" blood test measures four substances in your blood and screens for Down syndrome, trisomy 18 and neural tube defects such as spina bifida. ACOG notes that combining first- and second-trimester results is more accurate than a single test, though final results then arrive in the second trimester.

Glucose Screening (24–28 Weeks)

You drink a special sugar mixture and have blood drawn an hour later. A high level may be a sign of gestational diabetes, and ACOG says it should be followed by another type of glucose test to confirm. The screen may be done in the first trimester instead if you have risk factors for diabetes or had gestational diabetes before.

Rh Antibody Testing

If you are Rh negative and your baby could be Rh positive, ACOG's Rh factor guide says your ob-gyn may order an antibody screen in the first trimester and again at 28 weeks. Rh immunoglobulin, given as a shot at 28 weeks, stops the body from making Rh antibodies, which protects future pregnancies.

Third Trimester Testing

Group B Strep (GBS) Culture (36–38 Weeks)

A swab of the vagina and rectum checks for group B streptococcus, one of the many bacteria that live in the body; ACOG notes it usually does not cause serious illness in adults and is not an STI. It matters because GBS can pass to the baby during labor. That is rare — ACOG puts it at 1 or 2 babies out of 100 when the mother is not treated — but it can be very serious, so if your culture is positive, antibiotics are given through an IV once labor has started.

Non-Stress Test (NST)

If your pregnancy needs closer monitoring or goes past your due date, your provider may order non-stress tests, in which monitors track the baby's heart rate in response to the baby's own movements.

Biophysical Profile (BPP)

A biophysical profile pairs heart-rate monitoring with an ultrasound that looks at the baby's breathing movements, body movements, muscle tone and the amount of amniotic fluid. Your provider will explain the score and what, if anything, it changes. The third trimester guide covers these final weeks.

Genetic Testing Explained

Carrier screening is done on parents, or people thinking about becoming parents, using a blood sample or a cheek swab. It shows whether a person carries a gene for certain inherited disorders, and it can be done before or during pregnancy.

Amniocentesis is usually done between 15 and 20 weeks, though ACOG notes it can be done up until birth. A very thin needle, guided by ultrasound, withdraws a small amount of amniotic fluid. Results take from two days to several weeks depending on how the cells are analyzed. Leakage of fluid and slight bleeding can occur afterward and in most cases stop on their own.

CVS (chorionic villus sampling) takes a sample of tissue from the placenta. Its main advantage, in ACOG's words, is that it "is done earlier than amniocentesis, between 10 and 13 weeks of pregnancy." The trade-off is a slightly higher chance of miscarriage than with amniocentesis.

Making Testing Decisions

Prenatal testing is always optional. ACOG's wording is direct: "It is your choice whether to have prenatal testing." There is no right or wrong decision — it depends on your values, what information would help you, and how you would use the results.

Some people want every available test for maximum information and preparation time. Others prefer minimal testing. Many fall in between, choosing blood-and-ultrasound screening and keeping diagnostic procedures in reserve. Three questions help: What would I do differently with this result? Would knowing early help me prepare, or mainly make me anxious? Do I want a chance, or a definite answer?

A genetic counselor can help you understand your options, interpret results and work through the decision; ask your ob-gyn for a referral, and check with your insurer about coverage before the visit.

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Frequently Asked Questions

What does a "high risk" screening result mean?

It means the screening found a higher chance of a specific condition than in the general population — not that your baby has it. ACOG is equally clear about the reverse: a negative screen lowers the chance but does not rule the condition out. Diagnostic testing with CVS or amniocentesis gives a more definite answer and is an option for everyone. Your ob-gyn or a genetic counselor will go through your own numbers with you.

Is NIPT accurate?

NIPT (cell-free DNA testing) is a screening test, so it reports a level of risk, not a diagnosis. ACOG notes that every test can produce false-positive and false-negative results and that your health care professional can give you the rates for the specific test you are offered. ACOG also says a positive cell-free DNA result should be followed by a diagnostic test — amniocentesis or CVS.

When is each prenatal test done?

By ACOG's timings: routine blood and urine tests early in pregnancy; first-trimester screening at 10 to 13 weeks; cell-free DNA testing from 10 weeks; CVS at 10 to 13 weeks; amniocentesis usually at 15 to 20 weeks; the quad blood test at 15 to 22 weeks; the standard ultrasound at 18 to 22 weeks; glucose screening at 24 to 28 weeks; and the group B strep culture at 36 to 38 weeks.

Can I decline the glucose test?

You can decline any test, and ACOG states plainly that prenatal testing is your choice. The glucose screen is usually done between 24 and 28 weeks because a high blood sugar level may be a sign of gestational diabetes, which can cause problems during pregnancy. If the drink is the issue, tell your provider before the appointment and ask what alternatives their office accepts.

Are ultrasounds safe?

ACOG says there is currently no evidence that ultrasound is harmful to a developing fetus, and that no links have been found between ultrasound and birth defects, childhood cancer or later developmental problems. Because effects could still be identified in the future, ACOG recommends that ultrasound exams be done for medical reasons by qualified professionals. You should have at least one standard exam, usually at 18 to 22 weeks.