Third Trimester of Pregnancy: A Week-by-Week Guide

The third trimester of pregnancy is the home stretch — from week 28 all the way to birth. Your baby is growing fast and getting ready to meet you, while mom's body seems to change from one week to the next. In this guide we'll calmly walk through what happens in the third trimester: how your baby develops week by week, what you're likely to feel, which tests are coming up, which symptoms are perfectly normal and which are a reason to call your provider, and how to get ready for labor. If you're reading this short of breath, with swollen feet and a flutter of anxiety — you're doing just fine, and you're in good company with millions of other moms-to-be.

How many weeks is the third trimester, and when does it start?

Pregnancy is usually divided into three trimesters. The third trimester begins at week 28 and lasts until delivery. Most often the due date falls around 40 weeks, but a pregnancy is considered full term anytime between weeks 37 and 42. In short, the third trimester runs roughly from weeks 28 to 40 — about the last three months.

Doctors break the full-term window into a few stages, and this shapes how your care is managed:

• Before 37 weeks — if regular contractions begin, that's preterm labor, and your baby may need extra help.
• 37 weeks to 38 weeks and 6 days — early term.
• 39 to 40 weeks and 6 days — full term, the ideal window for birth.
• 41 weeks and beyond — late (post-term) pregnancy, which is watched especially closely.

Your due date is set from your last period and your first ultrasound, but remember: it's a guide, not a schedule. Only a small share of babies arrive exactly on their due date.

How your baby develops: the third trimester week by week

During the third trimester, your baby goes from a fragile little one to a newborn ready for life outside the womb. They put on weight, their lungs and brain "ripen," and they settle into a comfortable position before birth. The weight and length figures below are averages: your baby may be a bit bigger or smaller, and that's completely normal.

Weeks 28–31

Your baby weighs about 1–1.5 kg (roughly 2–3 lb) and measures 37–41 cm (about 15–16 in). The eyes now open and close, the skin smooths out, and the brain is developing quickly, forming new connections. The lungs are still immature, but they're starting to produce surfactant — a substance that helps the lungs expand after birth. Movements at this stage are strong and easy to feel.

Weeks 32–35

Weight climbs to about 1.7–2.5 kg (roughly 4–5.5 lb), and your baby is busy putting on body fat — they'll need it to stay warm after birth. The bones are hardening (except the soft skull bones, which stay flexible for delivery), and tiny nails are growing in. By now most babies have turned head down (cephalic position). If your baby is still bottom-down (breech), there's still time to turn, and your provider will keep an eye on it.

Weeks 36–40

By full term, your baby usually weighs 2.7–3.5 kg (roughly 6–7.5 lb) and grows to 48–52 cm (about 19–20 in). The lungs are nearly mature, and the organs are ready to work on their own. In the weeks before birth, many moms notice the belly "drop" as the baby's head nestles down toward the pelvis. Breathing gets a little easier, but pressure on the bladder and pelvic floor increases. This is one of the gentle early signs that labor is approaching.

What mom feels: how your body changes

Your growing uterus now fills most of your abdomen and crowds the organs around it, so the third trimester brings a whole bouquet of sensations. Almost all of them are a normal part of pregnancy — even if they're not the most pleasant.

• Shortness of breath. The uterus presses up against the diaphragm, making it harder to take a deep breath. It usually eases once the belly drops.
• Heartburn. Hormones relax the valve between the stomach and esophagus, and the uterus pushes on the stomach. Smaller, more frequent meals and skipping spicy or fatty foods at night can help — more in our article on heartburn during pregnancy.
• Swelling. Mild puffiness in the feet and ankles by evening is common. But sudden swelling of the face and hands along with a headache needs attention: when swelling is normal and when it's a reason to call your provider, we cover in a separate piece on swelling during pregnancy.
• Back and pelvic pain. Your center of gravity shifts and your ligaments soften under the influence of hormones. Gentle stretching, comfortable shoes, and back support all help — for more of what works, read our article on back pain during pregnancy.
• Frequent urination. Your baby presses on your bladder, so you'll need the bathroom more often, especially at night.
• Insomnia. Finding a comfortable position isn't easy, and thoughts of labor can keep you awake. The best position is on your side (usually the left) with a pillow between your knees; for more ideas, see our guide on how to sleep during pregnancy.
• Braxton Hicks contractions. Your uterus is "rehearsing": the belly tightens for a few seconds, then relaxes. They're irregular and usually painless — how to tell them apart from the real thing is in our article on Braxton Hicks contractions.

Movements: counting what's normal

Your baby's movements are your daily "report" on how they're doing. Closer to birth the pattern of movement changes: there's less room, so kicks feel different, but your baby shouldn't go quiet. Many providers suggest counting movements once a day in a calm setting: normally you'll feel about 10 distinct movements over a couple of hours. How this norm takes shape and what counts as enough activity is covered in detail in our article on normal fetal movement week by week. If your baby becomes noticeably calmer than usual, or you stop feeling movement — don't wait, contact your provider right away.

Tests and checkups in the third trimester

Visits to your provider become more frequent in the third trimester — first every two to three weeks, then weekly as you get closer to birth. Here's what you can likely expect:

• Ultrasound at 30–34 weeks. This checks your baby's growth and weight, the amount of amniotic fluid, the maturity and position of the placenta, and how your baby is lying.
• Doppler and CTG. Doppler shows blood flow in the vessels of the placenta and umbilical cord, while CTG (cardiotocography) records your baby's heartbeat and the tone of the uterus — a way to confirm your baby is comfortable.
• Complete blood count and iron levels. Anemia is often found in the third trimester, and your provider may recommend iron.
• Glucose monitoring. If you have risk factors, your blood sugar is checked to catch gestational diabetes early.
• Group B strep (GBS) swab. This is usually taken at 36–37 weeks. If the result is positive, you'll be given an antibiotic during labor to protect your baby — a standard and safe practice.
• Blood pressure and protein in your urine. These are checked at every visit so preeclampsia isn't missed.
• Weight gain. Your provider tracks the trend — what counts as healthy gain, we cover in our article on pregnancy weight gain.

As your due date nears, your provider will confirm your baby's position (head down or breech) — this shapes the plan for your delivery.

Warning signs: when to call your provider right away

Most third-trimester sensations are unpleasant but harmless. Still, there are signs that mean you should contact your provider or head to the hospital right away:

• A sharp drop in movement, or no movement at all — your baby has become noticeably quieter than usual.
• Vaginal bleeding (not to be confused with the mucus plug streaked with blood).
• Leaking or a gush of fluid from your waters — clear fluid that trickles or pours out.
• A severe headache, spots or flashes before your eyes, sudden swelling of the face and hands, pain in the upper right abdomen — possible signs of preeclampsia.
• Regular contractions before 37 weeks — these may signal preterm labor.
• Severe, constant abdominal pain, a high fever, fainting, or intense dizziness.

In situations like these, it's better to be safe and call than to wait. That's exactly what your care team is there for.

Signs labor is near: how to tell it's coming soon

In the days or weeks before birth, your body sends gentle signals — the early signs of labor. On their own they don't mean labor is happening today, but they hint that the finish line is close:

• The belly drops — breathing gets easier, but the downward pressure grows.
• Losing the mucus plug — a lump of thick mucus, sometimes streaked with blood. What it looks like and what it means is shown in our article on the mucus plug during pregnancy.
• Braxton Hicks contractions becoming more frequent and stronger.
• A pulling ache in your lower back and a crampy feeling low in your belly.
• A burst of energy and the "nesting instinct" — a sudden urge to clean everything and put it all in its place.

True labor is marked by regular, building contractions that come closer together and grow stronger and don't ease when you change position, along with your waters breaking. How to tell them apart from a false alarm and when it's time to head to the hospital is described in detail in our article on how to know labor has started.

Preparing for labor and the hospital

A calm birth often grows out of preparing ahead of time. Here's what's worth doing in the third trimester:

• Pack your hospital bag by week 36 — documents, and things for you and your baby. There's a ready-made list in our article with a hospital bag checklist.
• Think through your birth plan and discuss it with your provider: pain relief, who'll be with you, your wishes. A plan is a flexible guide, not a rigid script.
• Learn breathing and relaxation techniques — they help you move through contractions more calmly. Childbirth classes are a great help.
• Sort out the logistics — how and with whom you'll get to the hospital, and who's on call.
• Rest. Sleep and gentle walks matter more right now than a deep clean.

And one more thing: don't try to bring on labor yourself with folk remedies before your due date — if there's a medical reason, your provider will handle induction in a safe setting.

Key takeaways on the third trimester

• The third trimester runs from weeks 28 to 40; a pregnancy is considered full term from week 37.
• Your baby gains weight and fat, the lungs and brain "ripen," and by weeks 36–40 they usually settle head down.
• Shortness of breath, heartburn, swollen legs, back pain, insomnia, and Braxton Hicks contractions are a typical (and temporary) part of this stage.
• Track movements every day: a noticeable quieting of your baby is a reason to call your provider right away.
• Tests include ultrasound, CTG, blood pressure and urine protein checks, blood work, and a GBS swab.
• Bleeding, leaking waters, a severe headache with swelling and visual spots, and regular contractions before 37 weeks are signals to contact your provider right away.
• Pack your hospital bag and think through your birth plan ahead of time — preparation adds peace of mind.

This article is for general information only and is not a substitute for personalized medical advice. Always talk with your own OB-GYN about how you're feeling, your tests, and preparing for birth.