Third Trimester Guide: Weeks 28–40 of Pregnancy

Last updated: September 2026

The third trimester runs from week 29 to week 40, and it is the stretch where your baby roughly quadruples in weight, your prenatal visits move to every two weeks and then weekly, and the practical work of getting ready for labor and the first weeks home actually happens. According to the Office on Women's Health, your baby weighs about 4 to 4½ pounds at 32 weeks and about 6 to 6½ pounds at 36 weeks, and is considered full term at 39 weeks.

This guide covers how your baby grows week by week, what changes in your body and which of those changes are a reason to call, the tests and visits from 28 weeks on, how to prepare for labor, what to pack, how to set up for postpartum, and the warning signs that should never wait until morning. The one purchase that pays off from the first night of this trimester is a pregnancy pillow, because side sleeping with your belly and knees supported is what ACOG recommends for later pregnancy and what your hips will demand.

How Your Baby Grows in the Third Trimester

At the end of the second trimester your baby is about 12 inches long and weighs about 1½ pounds, per the Office on Women's Health. By birth, a full-term baby typically weighs somewhere between 6 pounds 2 ounces and 9 pounds 2 ounces and measures 19 to 21 inches. The table below is the OWH timeline for the weeks in between.

Movements change rather than stop as space runs out. From 28 weeks, the Office on Women's Health advises keeping track of your baby's movement so you notice if the baby is moving less than normal, which could be a sign of distress; pick the same time each evening, when babies tend to be most active, and get to know your baby's pattern.

Your Body in the Third Trimester

The Office on Women's Health lists the new changes most people notice now: shortness of breath, heartburn, swelling of the ankles, fingers and face, hemorrhoids, tender breasts that may leak colostrum, a belly button that sticks out, trouble sleeping, the baby "dropping" lower in your abdomen, and contractions that can be real or practice. Most of these come from a bigger baby pressing on your organs and ease after birth.

Practice contractions. Braxton Hicks contractions can happen for many weeks before real labor and can be painful enough to fool you, according to ACOG. The tells: false contractions have no pattern, do not get closer together, and may stop when you walk, rest or change position; true labor contractions come at regular intervals, get closer together, last about 60 to 90 seconds, and continue whether you rest or move.

Swelling. Some puffiness in the ankles and feet by evening is normal; put your feet up, keep moving during the day, drink water, and wear maternity compression socks if your legs feel heavy. Sudden or extreme swelling, especially of the face or hands, is different: OWH says to call your doctor right away because it can be a sign of preeclampsia, and ACOG lists it alongside a headache that will not go away, seeing spots, upper-abdominal pain and sudden weight gain as preeclampsia symptoms.

Sleeping in the Third Trimester

Sleeping on your side is best later in pregnancy, per ACOG's back pain guidance: keep one or both knees bent, place a pillow between your knees and another under your belly, or use a full-length body pillow. Insomnia is common rather than unusual; the Sleep Foundation reports at least 50 percent of pregnant women experience it. Eat dinner early to limit heartburn, taper fluids in the last hours before bed, and keep a nightlight on for bathroom trips. Our pregnancy sleep guide covers pillow setups and the fixes for restless legs, heartburn and leg cramps in detail.

Prenatal Visits and Tests From 28 Weeks

Routine checkups typically move to twice a month from 28 through 36 weeks and weekly from 36 weeks to birth, according to the Office on Women's Health; high-risk pregnancies are seen more often. At each visit expect blood pressure, weight, the baby's heartbeat and, later, a check of the baby's position.

Group B strep test. About 1 in 4 pregnant women carry group B strep, a common bacterium that can pass to the baby during birth, and ACOG says the swab test is done between 36 and 38 weeks (ACOG). If it is positive you receive IV antibiotics once labor starts, which greatly lowers the small risk to the baby. A positive result changes nothing about your birth plan except that you should head in a little earlier once contractions are regular.

Baby's position. A breech presentation, with buttocks or feet first, happens in 3 to 4 percent of full-term births per ACOG. If your baby is breech after 36 weeks, your provider may offer an external cephalic version (ECV), a hands-on attempt to turn the baby head down; more than half of ECV attempts succeed, though some babies turn back. If the baby stays breech, you and your provider will discuss the safest way to deliver.

Cervical checks. Your provider may check for dilation and effacement in the final weeks. Treat the number as a snapshot, not a forecast: you can be a few centimeters dilated for weeks or go from nothing to labor in a day. ACOG's definition is the useful one: as labor begins, the cervix opens and the uterus contracts at regular intervals.

Preparing for Labor and Delivery

Take a childbirth education class by week 32 so you finish before the weeks when sitting through one is hard. Hospital classes cover the stages of labor, pain relief options and what to expect on the day; Lamaze International offers online options if in-person schedules do not work. Write down your birth preferences afterward as a one-page communication tool rather than a script: pain relief, who is in the room, skin-to-skin, cord clamping, feeding plans. Our birth plan guide has a template, and the stages of labor guide walks through what each phase feels like.

Packing Your Hospital Bag

Pack by week 36. For you: a labor and delivery gown or robe that opens at the front for monitoring, skin-to-skin and the first feed; a nursing bra; a going-home outfit sized for the second trimester rather than pre-pregnancy; toiletries; a long phone charger; snacks; and comfort items such as your own pillow or a playlist. For the baby: a going-home outfit, a swaddle and a hat, with the car seat installed and inspected before labor. For your partner: a change of clothes, snacks, a charger and a pillow.

Documents matter as much as clothes: insurance card, ID, two copies of your birth preferences and a list of any medications you take. Most hospitals supply diapers, wipes and basic postpartum care for the stay, so confirm what yours provides before buying doubles. The full list is in our hospital bag checklist.

Setting Up for the First Weeks Home

The third trimester is when to prepare for the fourth. Stock the bathroom with postpartum pads, a peri bottle and witch hazel pads; set up a feeding station wherever you will sit most, with water, snacks, a nursing pillow and a phone charger within reach; and freeze a week of meals or line up the people who will bring them. If you plan to nurse, have nipple balm and breast pads ready before the milk comes in rather than sending someone out on day three.

A ready-made postpartum recovery box or breastfeeding box covers most of that list in one order and doubles as the thing to tell relatives to buy when they ask what you need. Our postpartum recovery essentials guide covers the full setup, and preparing for a cesarean is worth reading even if you do not expect one.

Warning Signs to Call About

Preterm labor (before 37 weeks). ACOG's signs of preterm labor are mild abdominal cramps with or without diarrhea, a change in vaginal discharge to watery, bloody or mucus-like, an increase in discharge, pelvic or lower abdominal pressure, a constant low dull backache, regular or frequent contractions or tightening that may be painless, and your water breaking. ACOG's instruction is not to wait: call your ob-gyn's office right away or go to the hospital.

Preeclampsia. Per ACOG, preeclampsia can develop quietly, and symptoms can include swelling of the face or hands, a headache that will not go away, seeing spots or changes in eyesight, pain in the upper abdomen or shoulder, nausea and vomiting in the second half of pregnancy, sudden weight gain, and difficulty breathing. Any of these, especially late in pregnancy, is a same-day call.

Also call right away for vaginal bleeding, a noticeable drop in your baby's movements compared with their usual pattern, a gush or trickle of fluid, or severe abdominal pain that does not ease. Call 911 for heavy bleeding, a seizure, difficulty breathing, or loss of consciousness.

Related Pregnancy Guides

The second trimester guide covers the weeks before this one, and the hospital bag checklist, birth plan guide and epidural guide cover the decisions of the next few weeks. For the nights in between, pregnancy sleep tips and the maternity clothes guide cover comfort from here to the due date.

Every symptom and timeline on this page is general guidance; your own provider's instructions for when to call and when to come in take precedence over anything written here.

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