By the second half of pregnancy, prenatal testing begins to feel different.
The early tests focus heavily on chromosomes and fetal development. Later tests are more likely to check how your body is handling pregnancy, how the baby is growing, and whether the placenta is continuing to support the baby well.
This is also when many pregnant patients encounter one of the most talked-about prenatal tests: the gestational diabetes screening.
Before each appointment, I found it helpful to know:
- Whether I needed to fast
- How long the test would take
- Whether I could eat or drink during the appointment
- What an abnormal result actually meant
- Whether I might need additional monitoring
Here is what to expect from common prenatal tests during the second and third trimesters in the United States.
This article is based on my personal pregnancy experience and general prenatal-care information. Your OB or maternal-fetal medicine specialist may recommend a different schedule based on your health and pregnancy.
Gestational Diabetes Screening
Most pregnant patients are screened for gestational diabetes between 24 and 28 weeks. Testing may be performed earlier if you have certain risk factors.
Gestational diabetes develops when pregnancy hormones make it harder for the body to use insulin effectively, causing blood sugar levels to rise.
Many OB practices in the United States use a two-step testing process:
- A one-hour glucose screening test
- A three-hour glucose tolerance test if the screening result is elevated
Some practices instead use a one-step, two-hour glucose tolerance test. Always follow the instructions from your own OB office because preparation and diagnostic criteria can differ.
The One-Hour Glucose Test
The first test is often called the one-hour glucose challenge test.
You will drink a sweet liquid containing glucose and have your blood drawn one hour later.
Do you have to fast?
Many practices do not require fasting for the one-hour screening, but this is not universal. Some offices provide specific instructions about what you may eat beforehand.
Do not change your diet or fast unnecessarily based on advice you see online. Ask your provider or laboratory for their exact instructions.
What does the glucose drink taste like?
The drink is very sweet and is often compared to a flat soda or concentrated fruit drink. The available flavor depends on the office or laboratory.
You will usually need to finish it within a set amount of time. Once you have started, you generally cannot eat, leave the testing area, or drink anything other than what the staff permits until the blood draw is complete.
Some people feel completely fine. Others may experience:
- Nausea
- Headache
- Dizziness
- Sweating
- Shakiness
- Fatigue after the initial sugar rush
If you vomit, tell the staff. The test may need to be rescheduled because your body did not retain the full glucose dose.
What if you fail the one-hour glucose test?
First, “failing” is not the best way to describe it.
An elevated result on the one-hour test does not automatically mean that you have gestational diabetes. It means your result was above your practice’s screening cutoff and you may need a diagnostic test.
The cutoff varies among laboratories and OB practices. That is why comparing your number with someone else’s result online can be confusing.
The Three-Hour Glucose Tolerance Test
If your one-hour result is elevated, you may be asked to complete a three-hour oral glucose tolerance test.
This test is more involved and usually requires fasting.
Your laboratory may ask you to avoid food for approximately 8 to 14 hours before the test. Follow its instructions about water, medication, supplements, and the exact time you should stop eating.
The appointment generally includes:
- A fasting blood draw
- Drinking a glucose solution
- A blood draw one hour later
- Another blood draw after two hours
- A final blood draw after three hours
Including check-in and waiting time, you may be at the laboratory for well over three hours.
What to bring
Consider bringing:
- A book, tablet, or headphones
- A phone charger
- A sweater or cardigan
- Water, if permitted by the laboratory
- A balanced snack to eat after the final blood draw
Do not eat your snack until the staff confirms that the test is finished.
If you become dizzy easily during fasting or blood draws, ask whether someone should drive you. Tell the staff immediately if you feel faint, severely nauseated, or unwell.
What if one or more numbers are high?
Your blood sugar is measured at several different times because your provider wants to see how your body processes the glucose over the entire three-hour period.
Gestational diabetes is commonly diagnosed when a specified number of values are above the laboratory’s limits, but the thresholds and interpretation can vary. Your OB should explain what your individual results mean.
If you are diagnosed with gestational diabetes, treatment may include:
- Nutrition changes
- Checking your blood sugar at home
- Physical activity when medically appropriate
- More frequent prenatal appointments
- Additional monitoring of the baby’s growth
- Medication or insulin when needed
A diagnosis does not mean that you did something wrong. Pregnancy hormones, genetics, placental function, and other factors all contribute to gestational diabetes.
Repeat Bloodwork in the Third Trimester
Your provider may repeat some blood tests later in pregnancy.
A complete blood count, or CBC, may be used to check:
- Hemoglobin and anemia
- Platelet levels
- Other blood-cell measurements
Anemia is relatively common during pregnancy because blood volume increases significantly. Depending on your results, your provider may recommend dietary changes, an iron supplement, or additional testing.
If you are Rh-negative, your provider may repeat an antibody screen and discuss Rh immune globulin, commonly known by the brand name RhoGAM.
Some patients are also retested for certain infections during the third trimester based on individual risk factors, state requirements, or office policy.
Blood Pressure and Preeclampsia Testing
Your blood pressure will be checked throughout pregnancy because preeclampsia can develop during the second half of pregnancy and sometimes after delivery.
If your blood pressure is elevated or you have concerning symptoms, your provider may order additional blood and urine tests.
These may include:
- Urine protein-to-creatinine ratio
- A 24-hour urine collection
- Platelet count
- Liver-function tests
- Kidney-function tests
Protein in the urine is one possible sign of preeclampsia, but it is not interpreted alone. Your provider will consider your blood pressure, symptoms, bloodwork, medical history, and the overall clinical picture.
Routine urine dipstick protein checks are not used in exactly the same way by every current prenatal practice. More specific testing may be ordered when there is a clinical concern.
Symptoms you should not ignore
Contact your maternity care team promptly if you develop:
- A severe or persistent headache
- Vision changes
- Pain in the upper abdomen, especially on the right side
- Sudden swelling of the face or hands
- Shortness of breath
- Nausea or vomiting later in pregnancy that feels unusual
- A concerning blood-pressure reading
- A sudden feeling that something is not right
Some swelling of the feet and ankles can be common in late pregnancy, but sudden or significant swelling—especially with other symptoms—deserves medical attention.
Preeclampsia evaluation may include urine protein, platelet, liver, and kidney testing, as described by ACOG’s patient guidance.
Third-Trimester Growth Ultrasounds
Not every patient receives routine growth ultrasounds during the third trimester.
They may be recommended when there are concerns or risk factors involving:
- The baby measuring smaller or larger than expected
- Gestational or preexisting diabetes
- High blood pressure
- Placental problems
- Amniotic-fluid levels
- Multiple pregnancy
- Previous pregnancy complications
- Certain high-risk pregnancies
During a growth ultrasound, the sonographer may measure the baby’s:
- Head
- Abdomen
- Femur, or thigh bone
- Estimated weight
- Position in the uterus
The scan may also evaluate placental location and amniotic-fluid volume.
The estimated fetal weight is exactly that—an estimate. Ultrasound measurements become less precise as pregnancy progresses, so the result should not be treated as the baby’s exact weight.
Your provider will usually pay attention to the baby’s growth pattern over time rather than relying on one number alone.
Group B Strep Test
Group B Streptococcus, commonly called GBS, is a type of bacteria that can naturally live in the digestive or genital tract.
GBS screening is generally performed near the end of pregnancy, usually between 36 and 38 weeks. ACOG’s clinical recommendation specifies universal screening at 36 weeks through 37 weeks and 6 days. ACOG explains GBS screening and treatment here.
What is the test like?
A healthcare professional uses a small swab to collect samples from the vagina and rectum.
The test:
- Takes only a few seconds
- Usually does not require a speculum
- Does not require fasting
- May be briefly uncomfortable but should not be painful
Some practices may allow patients to collect the sample themselves after receiving instructions.
What if the GBS result is positive?
Testing positive does NOT mean:
- You have a sexually transmitted infection
- You are unclean
- You did something wrong
- Your baby is already infected
GBS bacteria can come and go naturally.
If your result is positive, you will usually receive antibiotics through an IV during labor. The purpose is to reduce the chance of passing the bacteria to the baby during birth.
Because GBS can return after treatment, antibiotics are generally given during labor rather than trying to eliminate the bacteria weeks before delivery.
If you have a penicillin allergy, tell your provider before labor so the laboratory and care team can determine an appropriate antibiotic plan.
Nonstress Test
A nonstress test, or NST, monitors the baby’s heart rate and how it changes with movement.
Not everyone needs NSTs. They may be recommended because of:
- High blood pressure
- Diabetes
- Concerns about fetal movement
- A baby measuring small
- Low or high amniotic fluid
- Certain placental concerns
- Pregnancy continuing beyond the due date
- Other maternal or fetal risk factors
Because I was pregnant at age 40 and received high-risk monitoring, my appointment schedule included more fetal surveillance than someone with a low-risk pregnancy might receive.
What happens during an NST?
Two monitors are placed around your abdomen with soft elastic belts:
- One records the baby’s heart rate
- The other detects uterine activity
You may also be given a button to press when you feel the baby move.
An NST commonly takes about 20 to 40 minutes, but it may take longer if the baby is sleeping or the care team needs additional monitoring.
The test is called “nonstress” because it observes the baby without placing physical stress on the baby.
How to prepare
Usually, no fasting or special preparation is required. Unless your provider tells you otherwise, you can generally eat normally.
It can help to:
- Use the restroom before the test
- Wear a two-piece outfit that provides easy access to your abdomen
- Bring something quiet to read or listen to
- Allow extra time in case the baby is sleeping
If the initial tracing does not meet the expected criteria, it does not automatically mean something is wrong. The staff may continue monitoring, try to wake the baby, or order another assessment.
Biophysical Profile
A biophysical profile, or BPP, combines an ultrasound evaluation with an NST in some cases.
The ultrasound may assess:
- Fetal movement
- Muscle tone
- Practice breathing movements
- Amniotic-fluid volume
Each category contributes to an overall assessment of the baby’s well-being.
A modified BPP may include only an NST and an amniotic-fluid measurement. Which version you receive depends on the reason for monitoring and the practice’s protocol.
If a result is not reassuring, your provider may repeat the test, continue monitoring, or recommend delivery depending on your gestational age and the overall situation.
Kick Counts and Decreased Fetal Movement
Kick counting is not a laboratory or imaging test, but monitoring your baby’s usual movement pattern becomes increasingly important later in pregnancy.
There is no single movement pattern that feels identical for everyone. The goal is to become familiar with what is normal for your baby.
If your baby is moving significantly less than usual, follow your provider’s instructions and contact your maternity care team rather than waiting until the next appointment.
Do not rely on a home fetal Doppler to decide whether decreased movement is safe. Hearing a heartbeat at home cannot confirm that the baby is receiving enough oxygen or replace professional evaluation.
What I Learned About Late-Pregnancy Testing
Late-pregnancy appointments can become frequent, especially if you are seeing both an OB and an MFM specialist.
Before each test, confirm:
- Whether you need to fast
- Whether water is allowed
- How long you should expect to stay
- Where the test will be performed
- Whether you need a referral or insurance authorization
- What result would require follow-up
- When and how you will receive the results
Most importantly, a follow-up test does not automatically mean something is seriously wrong.
An elevated one-hour glucose result may simply mean you need the diagnostic test. An NST may take longer because the baby is sleeping. A repeat ultrasound may be needed because the sonographer could not obtain every required measurement.
Understanding the purpose of each test can make the final months of pregnancy feel much less intimidating.
Recommended Reading
(Disclosure: As an Amazon Associate, I may earn from qualifying purchases at no additional cost to you. I only recommend books, products, and resources that I have personally used, read, or genuinely believe may be helpful to my readers. Thank you for supporting Stateside Edit.)
A Simple Way to Organize Your Ultrasound Photos
By the time I reached the anatomy scan, I had collected ultrasound photos from several different appointments. An ultrasound photo album gave me one place to keep them in chronological order, along with the date and gestational week of each scan.
Because ultrasound printouts may fade over time, it is also a good idea to scan or photograph each image and save a digital copy. If you are choosing an album, look for acid-free, archival-quality pages designed to protect photos.
I found this (click here)👉ultrasound photo album helpful for keeping each scan together from the first trimester through the anatomy scan.
As an Amazon Associate, I earn from qualifying purchases.
Related Reading
When Is Your First Prenatal Appointment in the U.S.?
My Honest Experience Using an At-Home Fetal Doppler
What I Tell My Patients Before They Start Trying to Conceive
First Trimester Symptoms: What's Normal in Early Pregnancy? What I Experienced (and What I Wish Someone Had Told Me)
Second Trimester of Pregnancy: Feeling Better, Baby Kicks, and an Unexpected Illness
Third Trimester of Pregnancy: Preparing My Body, My Home, and My Mind for Birth
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