Screening tests offered in pregnancy in the US

What you are offered

Prenatal testing in the US divides into two categories that get confused constantly, and the distinction decides what a result means.

• Screening tests tell you the chance that a condition is present. They cannot confirm or rule it out.
• Diagnostic tests give a far more definite answer, and carry a small procedure-related risk.

ACOG's position is unambiguous: both screening and diagnostic testing are offered to all pregnant women. Diagnostic testing with CVS or amniocentesis is an option for everyone, not just those with a positive screen or an older maternal age. Equally, declining all of it is a legitimate choice, and ACOG says so — there is no right or wrong answer.

Routine laboratory tests

These are standard at the first prenatal visit and are not genetic screening:

• Blood type and Rh factor. If you are Rh negative and the fetus is Rh positive, your body can produce antibodies that damage fetal red blood cells. This rarely causes problems in a first pregnancy but can be serious in later ones. If you are Rh negative you may be given medication during pregnancy to prevent antibodies developing.
• Complete blood count, checking for anemia and other issues.
• Urinalysis and urine culture. The culture matters because urinary tract infections in pregnancy often produce no symptoms at all and still need treating.
• Hepatitis B and hepatitis C. Everyone should be tested for both. A vaccine protects the baby against hepatitis B, given as three shots with the first within a few hours of birth. You can breastfeed with either infection.
• HIV. Everyone is tested early. Medication during pregnancy greatly reduces the chance of transmission to the fetus.
• Syphilis — three times. ACOG advises testing at the first prenatal visit, again in the third trimester, and again at delivery.
• Chlamydia and gonorrhea, treated during pregnancy with retesting to confirm the treatment worked. Partners should be treated too.
• Tuberculosis for those at high risk — people with HIV, those in close contact with someone who has TB, and people from countries with high TB rates.

Genetic screening: your options by gestational age

Carrier screening — before or during pregnancy

Carrier screening is done on the parents, using a blood sample or a cheek swab, to find out whether either of you carries a gene for certain inherited disorders. It can be done before conception or during pregnancy, and doing it before is more useful because it widens your options.

Cell-free DNA — from 10 weeks

Cell-free DNA is a small amount of DNA released from the placenta into your bloodstream. A blood sample can be screened for Down syndrome and other aneuploidies from 10 weeks onward, with results in about a week. Note carefully: a positive cell-free DNA result should be followed by a diagnostic test with amniocentesis or CVS. It is a screening test with a strong reputation, not a diagnosis, and false positives happen.

First-trimester screening — 10 to 13 weeks

A blood test plus a nuchal translucency ultrasound measurement of fluid at the back of the fetal neck. Both parts are usually done together between 10 and 13 weeks.

Quad screen — second trimester

The quadruple or “quad” blood test measures four substances in your blood and screens for Down syndrome and other conditions. It is the fallback if you present too late for first-trimester options.

Diagnostic testing — CVS and amniocentesis

Chorionic villus sampling samples placental tissue; amniocentesis samples amniotic fluid. Both give a far more definite result and both carry a small risk. Your obstetric provider or a genetic counselor should quantify that risk for your specific situation before you decide.

Later-pregnancy screening

Glucose screening — 24 to 28 weeks

You drink a sugar solution and have blood drawn an hour later to measure glucose. A high result means a second, longer confirmatory test, not an immediate diagnosis. This may be done in the first trimester instead if you have risk factors for diabetes or had gestational diabetes previously.

Group B strep — 36 to 38 weeks

A swab from the vagina and rectum, cultured for group B streptococcus. A positive result means antibiotics in labor, not treatment now. This is a routine universal screen in the US, which is a real difference from the UK, where GBS is managed by risk factors rather than screening.

Anatomy ultrasound

A detailed ultrasound around 18 to 22 weeks examines fetal anatomy and growth.

Deciding what to have

ACOG suggests thinking ahead about how you would use a result. A positive screening test tells you only that you are at higher chance — a diagnostic test is needed for a more certain answer. Some parents want to know in advance in order to learn about the condition and plan medical care. Some do not want the information before birth and decline follow-up testing, or decline testing entirely. Some would consider ending the pregnancy in certain circumstances. All of these are recognised positions and your provider should not push you toward any of them.

One practical warning specific to the US: screening is not automatically covered by insurance. Cell-free DNA and expanded carrier panels in particular are frequently billed separately and can be expensive. Ask what a test costs and whether it is covered before it is drawn, not after.

Where to get help

The American College of Obstetricians and Gynecologists is the governing professional authority for prenatal screening in the US and publishes patient FAQs on both routine tests and genetic screening. A certified genetic counselor is the right person to talk to before or after any genetic test — they do not have a stake in your decision, and most obstetric practices can refer you. The National Society of Genetic Counselors maintains a directory of counselors who work directly with patients.