The third trimester brings you closer than ever to meeting your baby, and it is also a time when medical teams watch both of you more closely. Routine and sometimes extra tests help spot potential problems early, guide decisions about birth, and give you reassurance about how your pregnancy is progressing.
This guide explains the most common tests offered in the last three months of pregnancy, why they are done, what they are like from a parent’s point of view, and how to feel prepared each step of the way.
Why Testing Increases in Late Pregnancy
During the first and second trimesters, tests often focus on dating the pregnancy, screening for genetic conditions, and checking basic health. By the third trimester, the focus shifts more toward monitoring how your baby is growing and how your body is coping with the demands of late pregnancy.
- Doctors and midwives want to catch problems such as high blood pressure, infections, or growth concerns early, when they are easier to manage.
- Results from late pregnancy tests can help your care team plan for labor and delivery, including whether you might need medicines in labor or closer monitoring for you or your baby.
Not every parent will need every test. Your personal history, previous results, and any new symptoms all influence which tests are recommended.
Regular Checkups: The Foundation of Third Trimester Care
In the last three months, prenatal visits usually become more frequent. Many parents switch from appointments every four weeks to every two weeks, then weekly near their due date. These visits themselves involve several small but important checks that act as ongoing screening tests.
What Typically Happens at Each Visit
- Weight check: Helps your provider see how quickly you are gaining weight and whether sudden changes might point to fluid shifts or other health issues.
- Blood pressure: Monitored closely to spot signs of conditions like pregnancy-related high blood pressure or preeclampsia.
- Urine sample: Often checked for protein, sugar, or signs of infection, all of which can affect your health and your baby’s well-being.
- Belly measurement: The distance from the top of your uterus to your pubic bone (fundal height) gives a quick idea of your baby’s growth pattern.
- Baby’s heartbeat: A handheld device or brief monitor reading lets your provider hear your baby’s heart rate and rhythm.
Though these may feel routine, together they provide essential information and often guide whether any additional tests are needed.
Third Trimester Blood and Urine Tests
Even if you had many blood and urine tests earlier, some are repeated in late pregnancy because your body and risk factors can change over time. These tests usually require only a quick blood draw or urine sample.
Common Blood Tests in Late Pregnancy
- Complete blood count (CBC): Checks for anemia (low red blood cells), platelet levels, and other blood disorders that might affect fatigue, bleeding risk, or how you handle blood loss during birth.
- Infection screening: Some providers repeat tests for infections such as HIV or syphilis, especially if you were at higher risk or local guidelines recommend re-testing.
- Blood type and antibodies (when needed): If you have an Rh-negative blood type or certain antibodies, extra checks may guide whether you need an injection or additional monitoring.
Ongoing Urine Testing
- Protein in urine: Can signal possible kidney strain or preeclampsia when combined with high blood pressure.
- Sugar in urine: May point to issues with blood sugar control, especially if you have gestational diabetes or are being monitored for it.
- Signs of infection: White blood cells or bacteria in urine can indicate a urinary tract infection, which is important to treat in pregnancy.
These tests are typically brief, low risk, and give quick feedback about your current health status.
Gestational Diabetes Testing and Follow-Up
Most parents are screened for gestational diabetes in the second trimester. However, if you missed that window, had borderline results, or are at higher risk, your provider may order screening or follow-up testing in the third trimester.
Glucose Screening and Tolerance Tests
- Glucose screening test: You drink a sweet solution and have your blood sugar checked after a set time, often about one hour. If your level is above a certain threshold, you may need more detailed testing.
- Glucose tolerance test: Involves fasting, drinking a measured sugary drink, and having blood drawn several times over a few hours to see how your body processes sugar.
If gestational diabetes is diagnosed, ongoing blood sugar checks and occasional extra monitoring of your baby may be added to your care plan. The aim is to reduce the risk of complications, not to limit your enjoyment of pregnancy.
Group B Strep (GBS) Screening
Group B Streptococcus is a type of bacteria that can live harmlessly in the vagina or rectum of healthy adults, but may cause serious infection in newborns if passed during birth. Because of this, most pregnant people are offered a GBS test late in the third trimester, typically a few weeks before the due date.
How the GBS Test Works
- A small swab is gently rubbed around the vagina and rectum, either by you (with guidance) or your provider.
- The sample goes to a lab that checks whether GBS bacteria are present.
If the test is positive, it usually does not mean that you are sick. Instead, it tells the birth team to plan antibiotics through an IV during labor to help protect your baby from infection.
Ultrasound in the Third Trimester
Early ultrasounds often focus on dating the pregnancy and checking for major structural concerns. In the third trimester, ultrasounds are more targeted and may be ordered only when there is a specific question about your baby’s condition or your uterus and placenta.
Reasons for Late Pregnancy Ultrasounds
- Growth concerns: If fundal height measurements are smaller or larger than expected, an ultrasound may help confirm your baby’s size and growth pattern.
- Placenta and fluid check: Imaging can show where the placenta sits, how much amniotic fluid is present, and whether those findings fit what is expected at your stage of pregnancy.
- Position of the baby: Ultrasound can confirm whether your baby is head-down, breech, or in another position that might influence delivery options.
In some cases, ultrasound is combined with heart rate monitoring to create a more detailed picture of your baby’s well-being.
Nonstress Tests and Other Fetal Monitoring
When providers want closer observation of your baby’s health, especially in high-risk pregnancies, they may use external monitors to track your baby’s heart rate pattern and your contractions. These tests are noninvasive and usually done in a clinic or hospital setting.
Nonstress Test (NST)
- What it is: Two belts or sensors are placed on your belly—one to monitor your baby’s heartbeat and one to record uterine activity.
- What it measures: How your baby’s heart rate changes with movement, which can give clues about oxygen levels and overall well-being.
- How it feels: You may be asked to press a button when you feel your baby move, and the test usually lasts around 20–40 minutes.
Contraction-Based Tests and Biophysical Profiles
In some cases, additional tests may be suggested:
- Contraction tests: Your provider might check how your baby’s heart rate responds to contractions, either during natural contractions or ones gently stimulated by medication or nipple stimulation.
- Biophysical profile (BPP): Combines an ultrasound with heart rate monitoring to look at your baby’s breathing movements, body movements, muscle tone, and amniotic fluid volume.
These tests are most often used when your pregnancy carries higher risks, your baby’s movements have changed, or earlier tests raised questions that need more detail.
Pelvic Exams and Cervical Checks
As your due date approaches, your provider may offer pelvic exams to assess whether your cervix is starting to soften, thin, or open. These checks can give some information about how your body is preparing for labor, but they do not predict exactly when labor will start.
What to Expect During a Cervical Check
- You lie on an exam table and your provider gently inserts gloved fingers into the vagina to feel the cervix.
- They may describe your cervix in terms of dilation (how open it is), effacement (how thin it is), and the baby’s station (how low the head is in the pelvis).
Some parents prefer to limit or avoid routine cervical checks unless medically necessary. It is reasonable to ask whether an exam will change your care and to share your preferences.
Overview Table of Common Third Trimester Tests
| Test | Type of Test | Usual Timing | Main Purpose |
|---|---|---|---|
| Blood pressure, weight, urine dip | Office check | Every visit | Monitor parent’s health, screen for preeclampsia, infection, or sugar issues |
| Complete blood count (CBC) | Blood draw | Once in late pregnancy or as needed | Check for anemia and other blood-related problems |
| Gestational diabetes follow-up | Blood sugar tests | Late second to third trimester, or if risk factors appear | Diagnose or monitor blood sugar conditions |
| Group B Strep (GBS) swab | Vaginal and rectal swab | Late third trimester | Plan antibiotics in labor to protect baby from infection |
| Ultrasound | Imaging test | When growth, fluid, or position questions arise | Assess growth, fluid levels, placenta, and baby’s position |
| Nonstress test (NST) | External fetal monitoring | Usually in higher-risk pregnancies or when concerns arise | Evaluate baby’s heart rate pattern and well-being |
| Pelvic and cervical exam | Physical exam | Closer to due date or when indicated | Check cervical changes and baby’s position in the pelvis |
Talking With Your Provider About Tests
Good communication with your doctor or midwife helps each test feel less mysterious and more like a shared decision. You have the right to understand why a test is suggested, what it might show, and what choices you might face depending on the results.
- Ask whether the test is routine for everyone or recommended because of a specific concern in your pregnancy.
- Find out what happens if you decline a test, and whether there are alternative ways to monitor you or your baby.
- Take notes or bring a partner, friend, or support person who can help you remember information and ask questions.
Feeling informed and involved can make the testing process less stressful and help you feel more confident going into labor and birth.
Preparing Emotionally and Practically for Testing
Beyond the medical facts, third trimester tests can stir up many feelings—from relief that someone is watching closely to worry about what might be found. A bit of planning can make these appointments smoother and more comfortable.
- Plan for time: Some tests, like NSTs or glucose tolerance tests, take longer than a regular appointment. Arrange childcare, work coverage, or support ahead of time when you can.
- Bring comfort items: A snack (if allowed), water, and entertainment such as a book or playlist can help pass the time during longer tests.
- Use support networks: Share your concerns with trusted friends, family, or a prenatal support group. Hearing others’ experiences can help normalize what you are going through.
Remember that tests are tools, not judgments. Their role is to gather information that helps keep you and your baby as safe and healthy as possible.
Frequently Asked Questions (FAQs)
Do all pregnant people need every third trimester test?
No. While some checks, like blood pressure and urine tests, are standard at almost every visit, other tests are used only when there is a clear reason. Your medical history, pregnancy course, and preferences all guide which tests are recommended for you.
Can I refuse a test if I am uncomfortable?
Yes. In most cases, you can decline or delay a test after talking through the benefits, risks, and alternatives with your provider. It is helpful to ask how your care plan might change depending on whether you accept or decline a particular test.
Will more testing mean I have to have a cesarean birth?
Not necessarily. Some test results may lead your team to suggest certain options, like earlier delivery or continuous monitoring during labor, but many people with extra third trimester tests still have vaginal births. The key is discussing what each finding means for your specific situation.
How accurate are these tests?
Most third trimester tests are quite good at detecting broad patterns—such as whether blood pressure is rising, a baby is growing as expected, or there is an infection that needs treatment. No test is perfect, though, which is why providers often look at the whole picture, including your symptoms, exam, and more than one test over time.
What if a test result is abnormal?
An unexpected or abnormal result does not always mean something is seriously wrong. Sometimes it simply means that you will need repeat testing, extra monitoring, or a change in timing or location of birth. Keep asking questions until you understand what the findings mean for you and your baby.
Key Takeaways for Parents
- Third trimester tests focus on current health and safety, helping your team plan for a smoother labor and delivery.
- Common tests include regular blood pressure and urine checks, blood work, GBS screening, ultrasound, and fetal heart rate monitoring when indicated.
- You are an active partner in decision-making; it is always appropriate to ask why a test is suggested and how it may affect your care.
Understanding these tests can transform them from something to fear into useful tools that support you as you prepare to welcome your baby.
