Common Tests During Pregnancy and What They Screen For

Prenatal testing plays a crucial role in monitoring both maternal health and fetal development throughout pregnancy. These tests help healthcare providers identify potential complications early, screen for genetic conditions and birth defects, and guide decisions about care. Understanding what each test does and why it’s recommended helps you feel more prepared and informed at every appointment.

The tests you receive will be tailored to your individual situation, including your medical history, family background, age, and results from earlier screenings. Not everyone needs every test, and your healthcare provider will explain which ones apply to your pregnancy.

First Trimester Tests That Establish Your Pregnancy Baseline

The first trimester involves several foundational tests that provide essential information about your health and your baby’s early development. These initial screenings help identify any factors that might require monitoring or intervention as your pregnancy progresses.

1. Blood Type and Rh Factor Testing to Prevent Antibody Complications

One of the first blood tests you’ll receive determines your blood type (A, B, AB, or O) and Rh factor (positive or negative). This information is critical because of a condition called Rh incompatibility.

If you’re Rh-negative and your baby is Rh-positive (inherited from the other parent), your immune system might produce antibodies against your baby’s blood cells. This typically doesn’t affect a first pregnancy, but can cause serious problems in future pregnancies, including severe anemia, jaundice, brain damage, or even death in the baby.

If you’re Rh-negative, you’ll receive an injection of Rh immunoglobulin (RhoGAM) around 28 weeks and again within 72 hours after delivery if your baby is Rh-positive. This prevents your body from developing antibodies. You may also receive RhoGAM after any bleeding, amniocentesis, or trauma during pregnancy.

2. Complete Blood Count to Check for Anemia and Infections

A complete blood count (CBC) measures different components of your blood, including red blood cells, white blood cells, and platelets. This test screens for several conditions that can affect pregnancy.

The CBC helps identify:

• Anemia, which is common during pregnancy and can cause fatigue, weakness, and complications during delivery if severe
• Infections indicated by elevated white blood cell counts
• Clotting disorders that might increase bleeding risk during delivery
• Overall blood health that impacts oxygen delivery to your baby

You’ll likely have this test repeated in the third trimester, as anemia often develops later in pregnancy when blood volume increases significantly. If results show low iron levels, your provider may recommend iron supplements or dietary changes.

3. Infectious Disease Screening to Protect You and Your Baby

Early pregnancy includes screening for several infections that can be transmitted to the baby during pregnancy or delivery. These tests typically happen during your first prenatal visit.

Standard infectious disease screenings include:

• HIV testing because early detection and treatment dramatically reduce transmission risk to the baby
• Hepatitis B screening to identify chronic infection that can be passed during birth
• Syphilis testing as untreated syphilis can cause stillbirth, developmental delays, and serious health problems
• Rubella immunity testing to determine if you’re protected against German measles, which causes severe birth defects
• Chlamydia and gonorrhea screening (particularly for those under 25 or with risk factors) as these can cause preterm birth and eye infections in newborns

If any of these tests come back positive, treatment or preventive measures can significantly reduce or eliminate risks to your baby. Many of these infections can be managed effectively during pregnancy when caught early.

4. Carrier Screening for Inherited Genetic Conditions

Carrier screening determines whether you or your partner carry genes for certain inherited conditions. Being a carrier means you have one copy of a gene mutation but don’t have the condition yourself. If both parents are carriers of the same condition, there’s a 25% chance with each pregnancy that the baby will inherit both copies and have the condition.

Common conditions included in carrier screening:

• Cystic fibrosis, which affects the lungs and digestive system
• Sickle cell disease, which causes abnormal red blood cells and anemia
• Thalassemia, another blood disorder affecting hemoglobin production
• Spinal muscular atrophy, which affects motor neurons and muscle function
• Fragile X syndrome, which can cause intellectual disabilities

Expanded carrier screening panels can test for hundreds of conditions. Your ethnic background and family history help determine which conditions you’re at higher risk for. If screening shows you’re a carrier, your partner can be tested, and genetic counseling can help you understand the implications and options.

5. Early Ultrasound to Confirm Pregnancy Details

An early ultrasound, typically performed between 6 and 9 weeks, provides important baseline information about your pregnancy. This isn’t always medically necessary for low-risk pregnancies, but may be recommended in certain situations.

Early ultrasound helps:

• Confirm the pregnancy is developing in the uterus rather than being ectopic (in the fallopian tube)
• Determine accurate gestational age based on fetal measurements
• Identify whether you’re carrying twins or multiples
• Detect a fetal heartbeat, which is visible around 6 weeks
• Rule out miscarriage if there’s been bleeding or concerning symptoms

Accurate dating from early ultrasound is particularly important because it affects everything from screening test timing to determining if labor begins prematurely or goes past the due date.

6. First Trimester Screening for Chromosomal Abnormalities

First trimester screening, performed between 11 and 14 weeks, combines blood tests with a specialized ultrasound to estimate the risk of Down syndrome (trisomy 21) and trisomy 18 (Edwards syndrome).

The screening includes:

• Blood tests measuring pregnancy-associated plasma protein-A (PAPP-A) and human chorionic gonadotropin (hCG)
• Nuchal translucency ultrasound measuring fluid at the back of the baby’s neck

Abnormal results don’t mean your baby definitely has a condition, but indicate higher risk and the need for additional testing. This screening has a detection rate of about 85% for Down syndrome when combined with maternal age. If results are concerning, your provider will discuss diagnostic tests like CVS or amniocentesis that can provide definitive answers.

Second Trimester Tests That Monitor Growth and Development

The second trimester brings additional screenings that evaluate fetal anatomy in detail and continue monitoring your health. These tests build on earlier findings and can detect issues that weren’t visible in the first trimester.

7. Maternal Serum Screening for Neural Tube Defects and Chromosomal Conditions

Also called the quad screen or triple screen, this blood test is typically performed between 15 and 22 weeks. It measures multiple substances in your blood to assess risk for certain conditions.

The quad screen measures:

• Alpha-fetoprotein (AFP), which can indicate neural tube defects when elevated or chromosomal abnormalities when low
• Human chorionic gonadotropin (hCG), a pregnancy hormone
• Estriol, another pregnancy hormone
• Inhibin A, a protein produced by the placenta and ovaries

This screening can detect about 80% of neural tube defects like spina bifida and anencephaly. It also provides information about Down syndrome and trisomy 18 risk. Like first trimester screening, abnormal results indicate increased risk but aren’t diagnostic. Many people with abnormal results have healthy babies, while some with normal results still have affected pregnancies.

8. Anatomy Ultrasound to Examine Fetal Development

The anatomy ultrasound, performed between 18 and 22 weeks, is one of the most comprehensive prenatal tests. This detailed examination evaluates fetal organs, bones, and overall development.

During this ultrasound, the technician and physician examine:

• Brain structure and skull formation
• Heart chambers, valves, and major blood vessels
• Spine alignment and closure
• Abdominal organs including stomach, kidneys, and bladder
• Limbs and digits
• Facial features to check for cleft lip
• Placental position and amniotic fluid levels
• Fetal growth measurements

The anatomy ultrasound can detect many structural abnormalities, including heart defects, kidney problems, skeletal abnormalities, and neural tube defects. Finding these issues during pregnancy allows for planning specialized care at delivery, arranging for pediatric specialists to be present, or in some cases, considering fetal interventions or surgery.

This is also typically when parents learn the baby’s sex if they choose to know, though the primary purpose is medical evaluation.

9. Regular Urinalysis at Prenatal Visits

You’ll provide a urine sample at most prenatal appointments throughout your pregnancy. This simple test provides valuable information about several conditions.

Urinalysis screens for:

• Protein in urine, which can indicate preeclampsia, particularly when combined with high blood pressure
• Glucose in urine, which may suggest gestational diabetes
• Bacteria or white blood cells, which indicate urinary tract infections that can lead to preterm labor if untreated
• Ketones, which appear when your body isn’t getting enough carbohydrates

Many of these conditions don’t cause obvious symptoms initially, making routine urinalysis an important monitoring tool. Catching these issues early allows for treatment before they cause complications.

10. Glucose Tolerance Test for Gestational Diabetes Screening

Between 24 and 28 weeks, you’ll be screened for gestational diabetes, a form of diabetes that develops during pregnancy. This typically involves a two-step process, though some providers use a one-step test.

The standard screening process:

• One-hour glucose challenge test: You drink a glucose solution and have blood drawn one hour later. If results are elevated, you’ll need the second test.
• Three-hour glucose tolerance test: After fasting overnight, you have baseline blood drawn, drink a higher-dose glucose solution, then have blood drawn at one, two, and three hours afterward.

Gestational diabetes affects how your body processes sugar and can cause the baby to grow too large, increasing the risk of birth injuries during delivery, premature birth, breathing problems, and low blood sugar after birth. It also increases your risk of developing type 2 diabetes later in life.

If diagnosed with gestational diabetes, you’ll work with your healthcare team to manage blood sugar through diet, exercise, and sometimes medication. Most cases resolve after delivery, but you’ll need follow-up testing.

Third Trimester Tests That Prepare for Delivery

As you approach your due date, testing focuses on ensuring you and your baby are ready for labor and delivery. These final assessments help identify any last-minute complications that might affect delivery planning.

11. Group B Streptococcus Screening to Prevent Newborn Infection

Between 36 and 37 weeks, you’ll be screened for Group B streptococcus (GBS), a common bacteria that about 25% of pregnant people carry in their vagina or rectum. While GBS doesn’t usually cause problems for healthy adults, it can cause serious infections in newborns.

The screening involves a simple swab of the vaginal and rectal areas. If the test is positive, you’ll receive intravenous antibiotics during labor to prevent passing GBS to your baby during delivery. This reduces the newborn infection risk by about 80%.

Without treatment, babies exposed to GBS can develop:

• Sepsis (blood infection)
• Pneumonia
• Meningitis (brain and spinal cord inflammation)

These infections can cause serious complications or death, making GBS screening and treatment during labor crucial. A positive GBS test doesn’t mean anything is wrong with your pregnancy, and the antibiotics are safe and effective.

12. Repeat Complete Blood Count and Blood Pressure Monitoring

Your provider will repeat the CBC test in the third trimester to check for anemia, which commonly worsens as pregnancy progresses and blood volume increases. Significant anemia can cause complications during delivery, including excessive fatigue and increased risk with blood loss.

Blood pressure monitoring becomes even more critical in the third trimester as preeclampsia risk increases. Preeclampsia is a serious condition characterized by high blood pressure and protein in urine that typically develops after 20 weeks. Without treatment, it can cause:

• Seizures (eclampsia)
• Stroke
• Organ damage
• Placental abruption
• Preterm birth necessity
• Low birth weight

Regular blood pressure checks at every appointment help catch preeclampsia early. If you develop signs of preeclampsia, your provider will monitor you closely and may recommend early delivery depending on severity and gestational age.

13. Growth and Position Ultrasounds in Late Pregnancy

Additional ultrasounds in the third trimester aren’t routine for everyone but may be recommended based on your situation. These ultrasounds assess final preparations for delivery.

Late pregnancy ultrasounds evaluate:

• Fetal growth to ensure the baby is developing appropriately and identify if the baby is measuring much larger or smaller than expected
• Amniotic fluid levels since too much or too little can indicate problems
• Placental position to confirm the placenta hasn’t moved to cover the cervix (placenta previa)
• Baby’s position as delivery approaches, especially to identify breech position
• Fetal well-being through biophysical profiles that combine ultrasound with heart rate monitoring

If your baby is breech (feet or bottom first) after 36 weeks, your provider may discuss external cephalic version (manually turning the baby) or cesarean delivery. If growth concerns arise, closer monitoring or early delivery might be recommended.

Diagnostic Tests for High-Risk Pregnancies and Genetic Concerns

Beyond routine screenings, some pregnancies require additional diagnostic testing. These tests provide definitive answers rather than risk assessments, but they’re more invasive and carry small risks.

14. Cell-Free Fetal DNA Testing for Chromosomal Abnormalities

Also called non-invasive prenatal testing (NIPT), this blood test analyzes small fragments of fetal DNA circulating in maternal blood. It can be performed after 10 weeks and is more accurate than standard screening tests.

NIPT screens for:

• Down syndrome (trisomy 21)
• Trisomy 18 (Edwards syndrome)
• Trisomy 13 (Patau syndrome)
• Sex chromosome abnormalities
• Baby’s sex
• Some microdeletions (small missing pieces of chromosomes)

This test has a detection rate above 99% for Down syndrome and is increasingly offered to all pregnant people, though it’s particularly recommended for those with higher risk based on age, family history, or abnormal screening results. NIPT is highly accurate but is still a screening test, not diagnostic. Abnormal results should be confirmed with amniocentesis before making major decisions.

15. Chorionic Villus Sampling for Early Genetic Diagnosis

CVS is a diagnostic test performed between 10 and 13 weeks that can definitively diagnose chromosomal abnormalities and genetic conditions. It’s typically offered when there’s increased risk based on screening results, family history, or parental carrier status.

During CVS, a small sample of placental tissue is removed either through the cervix or through the abdomen using ultrasound guidance. The placental cells have the same genetic makeup as the fetus, allowing for chromosome analysis and genetic testing.

CVS can diagnose:

• Down syndrome and other chromosomal abnormalities
• Single-gene disorders like cystic fibrosis or sickle cell disease
• Some metabolic conditions

The procedure carries a small risk (about 1 in 455) of miscarriage. Results typically take 1-2 weeks, though preliminary results may be available within a few days. The advantage of CVS over amniocentesis is that it can be performed earlier in pregnancy, providing answers sooner.

16. Amniocentesis for Comprehensive Genetic and Developmental Testing

Amniocentesis is the most common diagnostic prenatal test, typically performed between 15 and 20 weeks. It involves removing a small amount of amniotic fluid using a thin needle guided by ultrasound. The fluid contains fetal cells that can be analyzed.

Amniocentesis can diagnose:

• Chromosomal abnormalities including Down syndrome and trisomy 18
• Neural tube defects through AFP measurement
• Genetic conditions when combined with molecular testing
• Fetal lung maturity in late pregnancy if early delivery is being considered
• Infections affecting the baby

The miscarriage risk is approximately 1 in 500 procedures. Most people experience only mild cramping afterward. Results usually take 1-2 weeks for full chromosome analysis, though rapid tests can provide preliminary results in 24-48 hours.

Amniocentesis might be recommended if you have abnormal screening results, a family history of genetic conditions, previous pregnancy with chromosomal abnormalities, or if you’re age 35 or older at delivery (though age alone is less commonly the sole reason given the availability of NIPT).

17. Additional Monitoring and Specialized Tests Based on Individual Risk

Some pregnancies require additional testing beyond the standard protocols. Your provider will recommend specific tests based on your medical history, pregnancy complications, or concerning findings.

Additional tests might include:

• Fetal echocardiography for detailed heart examination if there’s family history of heart defects or concerning anatomy ultrasound findings
• Doppler ultrasound to measure blood flow in the umbilical cord and fetal vessels if growth restriction is suspected
• Biophysical profile combining ultrasound assessment with fetal heart rate monitoring to evaluate well-being
• Non-stress test monitoring fetal heart rate and movement, typically used in high-risk pregnancies or past the due date
• Contraction stress test to see how the baby handles contractions
• Cervical length measurement to assess preterm labor risk in high-risk individuals

These additional tests help providers make informed decisions about pregnancy management, timing of delivery, and necessary interventions to ensure the best possible outcomes.

Understanding Your Test Results and Next Steps

Prenatal testing generates a significant amount of information throughout your pregnancy. Understanding what each test means and how results affect your care helps you feel more in control and less anxious about the process.

Remember that screening tests provide risk assessments, not diagnoses. An abnormal screening result doesn’t mean something is definitely wrong, just that additional testing is recommended. Many people with abnormal screening results have perfectly healthy babies. Conversely, screening tests can’t detect every problem, so normal results provide reassurance but not absolute certainty.

If you receive concerning results, your provider will explain what they mean, what additional testing or monitoring is recommended, and what your options are. Don’t hesitate to ask questions, request clarification, or seek a second opinion. This is medical information that may impact significant decisions, and you deserve to fully understand what you’re facing. Working closely with your healthcare team, asking about anything that’s unclear, and advocating for the care you need ensures you’re getting the most from prenatal testing.