Third Trimester of Pregnancy: Weeks 28–40 Guide

Baby Growth in the Third Trimester

The third trimester is about bulk and finishing touches: roughly half a pound a week of fat, plus the final wiring of the brain and lungs.

Weeks 28–32: Rapid weight gain

The brain forms deep grooves while billions of neurons connect. The lungs produce surfactant, which keeps air sacs open after the first breath. The baby practices breathing, swallowing, and thumb-sucking, and most babies turn head-down by week 32.

Weeks 33–36: Systems come online

Bones harden (except the skull, which stays flexible for birth) as kidneys and liver mature. The vernix coating and fine lanugo hair mostly disappear. Babies born at 34–36 weeks — “late preterm” — usually do well but may need help feeding and staying warm.

Weeks 37–40: Full term and ready

At 37 weeks the baby is early term; 39–40 weeks is full term, when lungs, brain, and liver are at their best. The head engages in the pelvis (“dropping”), and movements feel more like rolls than kicks as space runs out.

Kick Counts and Fetal Monitoring

Once movements are regular — usually by week 28 — paying attention to them becomes one of the simplest and most powerful things you can do. You know your baby's pattern better than any monitor: when they are active, how vigorous they are, what a typical day feels like.

How to count kicks

Choose a time your baby is usually active, lie on your side, and count every distinct movement — kicks, rolls, jabs, and swishes all count. Many providers use “10 movements within 2 hours” as a benchmark, but consistency with your baby's normal matters more than the exact number.

Non-stress tests and ultrasounds

From around week 32 — earlier for high-risk pregnancies — providers may order non-stress tests (NSTs), which monitor the baby's heart rate during movement for about 20 minutes, or biophysical profiles combining an NST with ultrasound checks. These are routine, painless surveillance tools.

When movement changes

Call your provider the same day if movements slow noticeably, stop, or feel very different from usual — do not wait for the next appointment. Most evaluations turn out fine, but decreased movement is one of the few symptoms where acting fast genuinely changes outcomes.

Common Third Trimester Symptoms

The third trimester is physically demanding — there is no way around a uterus the size of a watermelon. Knowing which discomforts are standard-issue (and what helps) makes the final weeks more bearable.

Sleep, breathing, and bathroom trips

Side-lying with pillows between the knees, under the belly, and behind the back is the classic sleep setup. Shortness of breath is common as the uterus presses the diaphragm upward, and the baby's head on your bladder means frequent nighttime bathroom trips.

Swelling, back pain, and heartburn

Mild ankle and foot swelling is typical by evening — elevating your feet and staying hydrated help. Back pain peaks now; warm baths and a belly band offer relief. Heartburn intensifies as the stomach gets crowded: smaller meals and sleeping propped up help.

Braxton Hicks and pelvic pressure

Irregular, painless tightenings — Braxton Hicks — often increase now. They are your uterus rehearsing, and they typically fade with rest or hydration. Growing pelvic pressure and the occasional sharp twinge reflect the baby settling lower. Uncomfortable, but usually normal.

Birth Planning: Choices to Consider

A birth plan is not a script — labor rarely follows one — but writing it forces you to learn your options before you are in the middle of contractions. Keep it to one page, share it with your provider ahead of time, and frame everything as preferences.

Labor and delivery preferences

Consider who you want in the room, freedom to move and change positions, pain relief options (from breathing techniques to epidural), and how you feel about interventions like induction or cesarean birth if needed. Touring your hospital or birth center beforehand answers half these questions.

After birth and practical prep

Note your “golden hour” wishes — skin-to-skin contact, delayed cord clamping, feeding plans — then handle logistics by week 36: pack the hospital bag (ID, birth plan, clothes, toiletries, charger, snacks, baby's going-home outfit), install the infant car seat and get it inspected, and line up postpartum help for meals and household basics.

Signs of Labor: Real vs. False

True labor has a signature — contractions that get longer, stronger, and closer together and do not ease with rest. False labor (Braxton Hicks) is irregular, often stays mild, and typically fades when you change position or hydrate.

The classic signs

Regular, intensifying contractions are the headline act. Your water breaking — a gush or a steady trickle of fluid — is another; call your provider when it happens and note the time, color, and amount. Bloody show (mucus tinged pink or brown) often precedes labor by hours or days.

When to head in

First-time parents often use the 4-1-1 rule: contractions every 4 minutes, lasting 1 minute each, for at least 1 hour. Go in sooner if your water breaks, you have heavy bleeding, or the baby's movements decrease. For later births, leave earlier — subsequent labors commonly progress faster.

Week-by-Week: Weeks 28–40

The final stretch, week by week: kick counts begin, the GBS test arrives, the baby drops, and full term begins. Jump to your current week in our week-by-week pregnancy guide below.

Double-check your countdown with our due date calculator.

When to Call Your Doctor

In the third trimester, the threshold for calling is low — providers expect frequent questions now. Call immediately for decreased or absent fetal movement, vaginal bleeding, fluid leaking from the vagina, regular contractions before 37 weeks, severe headache, vision changes, sudden swelling of the face or hands, severe abdominal pain, or fever.

Severe headache, vision changes, and sudden swelling can signal preeclampsia. Regular contractions before 37 weeks may indicate preterm labor, which can sometimes be slowed when caught early.