Prenatal Tests: Types, Timing, and What Results Mean

During pregnancy, your health care team may offer a variety of prenatal tests. These tests provide information about your health and your baby’s development before birth, helping you make informed decisions about your pregnancy and delivery.

This guide explains the main types of prenatal tests, when they are usually done, what they can and cannot tell you, and how to think through your options.

What Are Prenatal Tests?

Prenatal tests are medical tests done in pregnancy to:

• Check the overall health and development of the fetus
• Monitor the pregnant person’s health and pregnancy-related conditions (for example, anemia or gestational diabetes)
• Estimate the chance of certain genetic or structural conditions in the fetus

Some tests are recommended for nearly all pregnancies, while others are offered based on age, family history, previous pregnancies, or specific risk factors.

Screening vs. Diagnostic Tests

Most prenatal testing falls into two broad categories.

An abnormal screening test result means more information is needed, not that a problem is definitely present. In that situation, your provider may discuss follow-up imaging, repeat screening, or diagnostic testing.

Common Routine Tests in Pregnancy

Alongside genetic and structural screening, prenatal care includes routine tests that focus on the pregnant person’s health and on general fetal well-being.

Blood and Urine Tests

Early and periodic tests may include:

• Blood type and Rh factor: Helps identify Rh incompatibility, which can affect future pregnancies if untreated.
• Complete blood count (CBC): Screens for anemia and certain infections.
• Infection screening: Tests for conditions such as hepatitis B, HIV, and syphilis, because early treatment can protect both parent and baby.
• Urine tests: Check for protein, sugar, and signs of infection that can point to kidney problems, urinary tract infection, or preeclampsia.

Gestational Diabetes Screening

Most pregnant people are offered a glucose screening test between about 24 and 28 weeks of pregnancy to check for gestational diabetes. This usually involves:

• Drinking a sweet solution
• Having blood drawn after a specified period to see how the body handles sugar

If results are elevated, a longer glucose tolerance test may be recommended to confirm whether gestational diabetes is present.

Blood Pressure and Weight Checks

At most prenatal visits, your blood pressure and weight are checked. Elevated blood pressure can be an early sign of hypertensive disorders of pregnancy, including preeclampsia, which require careful monitoring.

Genetic Carrier Screening (Before or Early in Pregnancy)

Carrier screening is a blood test that looks for certain inherited genetic conditions that parents can pass on to a child.

These tests are often offered:

• Before pregnancy (ideally)
• Early in pregnancy, if not done earlier

Carrier screening commonly evaluates risk for conditions such as:

• Cystic fibrosis
• Spinal muscular atrophy
• Sickle cell disease and some other hemoglobin disorders

If one partner is found to be a carrier, the other partner may also be offered testing. When both partners carry a change in the same gene, there is a higher chance that a child could inherit that condition.

First-Trimester Screening Options

In the first trimester, your provider may discuss tests that estimate the chance of certain chromosomal conditions and some structural differences.

Blood Tests and Ultrasound-Based Screening

First-trimester screening can combine:

• Blood tests to measure specific substances in the pregnant person’s blood
• Ultrasound measurements, such as the thickness of the fluid at the back of the fetus’s neck (known as nuchal translucency)

These results, along with factors like age, are used to calculate a risk estimate for certain conditions, such as trisomy 21 (Down syndrome) and trisomy 18.

Noninvasive Prenatal Testing (NIPT) / Cell-Free DNA

Cell-free DNA (cfDNA) testing, often called noninvasive prenatal testing (NIPT), analyzes small fragments of placental DNA that circulate in the pregnant person’s blood.

Key points about cfDNA/NIPT:

• Usually offered from about 10 weeks of pregnancy onward
• Estimates risk for certain chromosomal conditions, including trisomy 21, trisomy 18, and trisomy 13
• Can usually determine fetal sex, if desired
• Is a screening test, not a diagnostic test; abnormal results are typically confirmed with CVS or amniocentesis

Second-Trimester Screening and Imaging

In the second trimester, many people are offered additional screening tests and detailed ultrasound imaging.

Maternal Serum Screening

Second-trimester blood tests may measure several substances in the pregnant person’s blood to estimate the chance of:

• Certain chromosomal conditions (for example, trisomy 21)
• Some brain and spinal cord abnormalities, such as open neural tube defects

This type of test is sometimes called a triple or quad screen, depending on how many markers are included.

Ultrasound for Anatomy Assessment

A detailed ultrasound, often done around the middle of pregnancy, evaluates:

• Fetal growth and anatomy (organs, limbs, spine, and facial structures)
• Placental position
• Amniotic fluid level
• Number of fetuses and their positions

Ultrasound can detect many structural differences and may suggest the need for further testing if something unexpected is seen.

Diagnostic Tests: CVS and Amniocentesis

If a screening test result shows an increased chance of a condition—or if there is a strong family or personal history—your provider may discuss diagnostic testing.

Chorionic Villus Sampling (CVS)

CVS involves collecting a small sample of placental tissue, usually between about 10 and 13 weeks of pregnancy.

The sample is examined in a laboratory to look at chromosomes and, in some cases, for specific genetic conditions. CVS:

• Provides diagnostic information earlier in pregnancy than amniocentesis
• Has a small risk of complications, including miscarriage

Amniocentesis

Amniocentesis typically takes place later in pregnancy (often after 15 weeks).

Using ultrasound guidance, a thin needle is used to take a small sample of amniotic fluid. The cells in the fluid are analyzed to look for chromosomal conditions, and sometimes specific genetic or biochemical conditions. Amniocentesis:

• Is considered a diagnostic test for many chromosomal conditions
• Carries a small risk of pregnancy loss and other complications

Why Prenatal Testing Is Offered

Prenatal testing is a personal choice, but it can offer several potential benefits.

• Information and preparation: Knowing about certain conditions before birth gives families and providers time to plan delivery location, medical support, and early treatments when available.
• Reassurance: When results are reassuring, many parents feel less anxious about the pregnancy.
• Decision-making support: Some families use this information to reflect on pregnancy and delivery options, including the type of care team they want at birth.
• Monitoring parental health: Tests for anemia, infections, blood pressure issues, and gestational diabetes allow early treatment to support a healthy pregnancy.

Considerations, Limitations, and Risks

It is helpful to understand what prenatal tests cannot do, as well as the potential downsides.

Limits of What Tests Can Detect

• Screening tests provide risk estimates, not certainties.
• Even diagnostic tests cannot identify every possible difference or future health concern.
• Some conditions only become apparent later in pregnancy, after birth, or during childhood.

False Positives and False Negatives

• A screening test may suggest an increased chance of a condition when the fetus is unaffected (false positive).
• Occasionally, a screening test may miss an existing condition (false negative).
• Because of these possibilities, abnormal screening results are often followed by diagnostic testing for clarity.

Procedure-Related Risks

Diagnostic tests like CVS and amniocentesis have a small risk of miscarriage and other complications, such as cramping, bleeding, or infection. Your provider or genetic counselor can explain current estimates for these risks at your specific center.

Who Might Be Offered More Extensive Testing?

Anyone can choose to have or decline many types of prenatal testing, but certain factors may lead providers to offer more detailed screening or diagnostic options.

• Age 35 or older at the estimated time of delivery
• Previous pregnancy affected by a chromosomal or genetic condition
• Family history of specific inherited conditions
• Certain ultrasound findings
• Positive or concerning results on prior screening tests

Genetic counseling is often recommended in these situations to help families understand options and possible outcomes.

Key Questions to Ask Your Health Care Provider

Before deciding about any prenatal test, consider asking:

• What is the goal of this test? Is it screening or diagnostic?
• What specific conditions does it look for?
• How accurate are the results? What are the chances of false positives or false negatives?
• What are the risks or side effects? Are there safer alternatives?
• How will the results change my care? Will they affect monitoring, delivery plans, or treatment options?
• What follow-up will be recommended if the result is abnormal?

Emotional and Practical Support

Waiting for or receiving test results can be emotionally challenging. It may help to:

• Talk openly with your partner or support system about your values and concerns
• Ask your provider for referrals to counseling or support groups if you receive unexpected news
• Meet with a genetic counselor for detailed explanations of risks, options, and possible next steps

Remember that you can usually take time to ask questions and consider your choices before moving forward with more testing.

Frequently Asked Questions (FAQs)