Third Trimester Guide · Weeks 28–40
The final stretch. Baby gains roughly half a pound a week, lungs finish maturing, kicks shift to rolls as space tightens, and weekly prenatal visits begin around week 36 as the body prepares for birth. Here's exactly what happens each week, and exactly what to do about it.
The third trimester covers weeks 28 through 40 — the moment your second trimester ends through your due date (and a couple of weeks beyond, since only a small fraction of babies arrive exactly on their EDD). It is the most physically demanding trimester, the most logistically active, and the one where most of the hands-on birth preparation happens.
Baby gains roughly half a pound per week from week 31 onward. Lungs finish maturing through the production of surfactant — the substance that lets the air sacs actually expand. Movements shift in character: the jabs and kicks give way to slower rolls, stretches, and visible belly-shifting as space tightens. Many babies settle head-down into the pelvis somewhere between weeks 32 and 38, a process called engagement.
Symptoms intensify in the third trimester. Heartburn peaks around weeks 29–30. Backaches, pelvic pressure, swelling, shortness of breath, and difficulty sleeping are common enough to feel universal. The practical work of the trimester splits into two phases: weeks 28–35 are about preparation (kick counts, birth preferences, hospital bag, choosing pediatricians, prepping leave) and weeks 36–40 are about waiting (Braxton Hicks, signs of true labor, weekly visits). Learning to tell preterm-labor signs from Braxton Hicks, and labor from "almost labor," is part of the work of these weeks.
This guide pulls week-by-week milestones, symptoms, and self-care tips from the same Erin-vetted dataset that powers the Pregnancy Tracker. Pick any week 28–40 to see exactly what's happening with your baby and what to focus on. For a full tracker with notes, kick counts, contractions, and 24/7 doula chat, jump to the Pregnancy Tracker at the bottom of the page.
Week 28 · Trimester 3
Week 29 · Trimester 3
Week 30 · Trimester 3
Week 31 · Trimester 3
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Week 40 · Trimester 3
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When does the third trimester start?
The third trimester starts at week 28, the moment the second trimester ends. It runs through delivery, typically around week 40 (with 37–42 considered the normal range). The medical convention is that the first trimester covers weeks 1–13, the second trimester covers weeks 14–27, and the third trimester covers weeks 28 through birth. Babies born at 37 weeks or later are considered 'full term,' with 39–40 weeks as the most common window for spontaneous labor to begin.
When should I start kick counts?
Most providers recommend starting formal kick counts around week 28. The standard protocol is to pick a time of day when baby is usually active, sit on your left side or in a comfortable position, and count distinct movements (kicks, rolls, stretches — not hiccups) until you reach 10 within a 2-hour window. Most people reach 10 well under that, often within an hour. After week 32, you should also check in on patterns daily — babies typically have busy and quiet periods, but a sudden or persistent decrease warrants a call to your provider.
What's the difference between Braxton Hicks and real contractions?
Braxton Hicks contractions are irregular, infrequent, and usually painless (a tightening that releases within a minute or so). They often ease with hydration, position change, or rest. Real labor contractions grow progressively closer together, longer, and stronger — coming at regular intervals regardless of activity, and not easing with rest or hydration. Other signs of true labor include a bloody show, water breaking (a gush or continuous trickle of fluid), and persistent lower back pain or cramping. If you're unsure whether what you're feeling is real labor, time them for an hour and call your provider with what you observe.
When do weekly prenatal visits begin?
For most low-risk pregnancies, prenatal visits happen every four weeks through week 28, every two weeks from weeks 28 through 35, and then weekly from week 36 until delivery. The cadence may shift earlier or more often if your pregnancy is considered higher-risk (twins, preeclampsia history, gestational diabetes, etc.). Weekly visits in the final month typically include checking baby's position, fetal heart rate, and your blood pressure, and screening for Group B Strep around weeks 36–37.
What should be in my hospital bag by week 36?
By week 36 it's wise to have a bag packed and by the door (or in the car). Essentials: photo ID and insurance card, your birth preferences sheet, two pillows, a phone charger (long cord), comfortable going-home outfit for you and for baby, snacks that hold up without refrigeration, a refillable water bottle, your own labor-friendly items (a robe, slippers, hair ties), a nursing bra if you plan to breastfeed, and any comfort items for your support person. For baby: a car seat (already installed and inspected), a few onesies, a blanket, and diapers. Less is more — most people over-pack and never open half of it.
When should I call my provider about decreased movement?
Call your provider any time you notice a persistent or sudden decrease in baby's movement, especially after week 28. Practical steps: drink something cold and sugary, lie on your left side, and count movements for two hours. If you don't reach 10 distinct movements in that window — or if movement feels meaningfully reduced compared to baby's typical pattern — call your office (most have an after-hours line) or go to labor and delivery. Reduced movement can be an early sign of distress, and providers would rather see you for a reassuring check than miss something real.