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Third Trimester
Weeks 28–40+ — the home stretch
What's Happening With Baby
- The third trimester runs from week 28 until birth — typically around 12–13 weeks, though of course it ends whenever baby decides to arrive.
- Baby spends this trimester primarily gaining weight and maturing — lungs, brain, and other systems continue developing right up until delivery, which is part of why full-term is defined the way it is.
- Movement patterns become more established, and providers will ask you to start paying attention to your baby's typical activity level.
Source: Cleveland Clinic, "Third Trimester of Pregnancy"
What's Happening In Your Body
- Shortness of breath, backaches, and more frequent urination are the hallmark symptoms as baby takes up more room and puts pressure on your diaphragm and bladder.
- Swelling in the feet and ankles is common; sudden or severe swelling, especially in the hands or face, is not — see the warning signs below.
- Braxton Hicks contractions (irregular, usually painless tightening) can start showing up as your body practices for labor.
- Trouble sleeping, heartburn, and pelvic pressure tend to intensify as your due date approaches.
Source: Cleveland Clinic; Mayo Clinic
Your Prenatal Care in the Third Trimester
Visits get noticeably more frequent from here:
- Every four weeks until about week 28
- Every two weeks from 28–36 weeks
- Weekly from 36 weeks until delivery
At each visit, expect blood pressure and weight checks, fundal height measurement, fetal heart rate, a urine sample, and a conversation about any new symptoms, contractions, or fluid changes.
Key third-trimester tests and vaccines:
- Group B Strep (GBS) test, done between weeks 36–37 (ACOG's current window; some sources cite up to 38 weeks). This is a simple swab of the vagina and rectum. GBS is common and usually harmless in adults — it's not an STI and doesn't mean anything went wrong — but it can be serious for a newborn if untreated. If you test positive, you'll receive IV antibiotics (usually penicillin) once labor starts, which is highly effective at protecting baby.
- Tdap vaccine, recommended between weeks 27–36.
- Flu, COVID-19, and RSV vaccines may also be recommended depending on timing and your provider's guidance.
- Gestational diabetes screening, if not already completed, along with a follow-up glucose challenge test if needed.
Your provider will also start talking through what to expect during labor, when to head to the hospital, and hospital registration — a good time to ask every question you've been saving up.
Source: Mayo Clinic, "Prenatal Care: Third Trimester Visits"; ACOG, "Group B Strep and Pregnancy"; UPMC
When to Call Your Provider (or Go In)
- Regular contractions occurring every five minutes or closer
- Any vaginal bleeding
- Fluid leaking (possible water breaking)
- Severe or persistent headache, especially with vision changes — a possible sign of preeclampsia
- Sudden swelling in your face or hands
- A noticeable decrease in baby's movement
Source: UPMC; Mayo Clinic
FAQs
Is Group B Strep something I did wrong?
No. GBS is naturally present in many healthy adults and isn't related to hygiene or anything you could have prevented — it's simply routine to test for and treat during labor if present.
Why are my appointments suddenly so much more frequent?
Your provider is watching more closely for things like preeclampsia and monitoring baby's growth and position as delivery approaches — it's standard care, not a sign of concern by itself.
What if I go past my due date?
Due dates are estimates, not deadlines. Your provider will discuss monitoring and, if needed, induction timing based on your specific situation.
"The last stretch asks the most of your body — and it's the same body that's been doing this all along."