Third Trimester: Your Weeks 28 to 40 Guide
Reviewed by Safi Allah Khan
Medically reviewed by: Safi Allah Khan · Written by the Momi team · Last updated 20 October 2026
Quick answer: The third trimester is the final stage of pregnancy, from 28 weeks until birth, roughly months 7 to 9. Your baby gains weight fast and gets ready for life outside the womb. Common symptoms include tiredness, heartburn, backache, poor sleep and Braxton Hicks. Learn your baby's movement pattern and the signs of labor.
Find your week with How Many Weeks Pregnant Am I?, or follow along week by week from 28 weeks pregnant.
Third trimester at a glance
| Week | What usually happens |
|---|---|
| 28 | Third trimester starts; sleep on your side from now; checks become more frequent |
| 28–32 | Baby's movements are strong and regular; anti-D or vaccines if offered |
| 32–34 | Baby often settles head down; birth plan conversations |
| 34–36 | Pack your hospital bag; check when to call in labor |
| 36 | Position check; appointments often weekly |
| 37 | Early term |
| 39–40 | Full term; estimated due date at 40 weeks |
| 41–42 | Late term; induction may be discussed |
Your baby's growth
ACOG describes the third trimester as the time when the fetus gains weight and the organs mature, ready to work after birth. Mayo Clinic notes the lungs and brain are still maturing through these weeks.
| Week | Approximate size | Development |
|---|---|---|
| 28 | About 1 kg (2.2 lb) | Eyes can open; sleep and wake cycles |
| 32 | About 1.7 kg (3.75 lb) | Gaining fat; bones hardening |
| 36 | About 2.6 kg (5.8 lb) | Lungs nearly mature |
| 40 | About 3.4 kg (7.6 lb) | Ready for birth |
These are averages; healthy babies vary a lot. For every week, see baby size by week.
Common third trimester symptoms
| Symptom | Why it happens | What helps |
|---|---|---|
| Tiredness | Carrying extra weight, poor sleep | Rest, naps, accept help |
| Heartburn | Baby pressing on your stomach, hormones | Smaller meals, sit up after eating |
| Backache and pelvic pain | Posture changes, loosening joints | Flat shoes, support, physio if severe |
| Trouble sleeping | Bump, peeing at night, cramps | Pillows, side sleeping; see pregnancy insomnia |
| Braxton Hicks | Practice tightenings | Rest and change position; they ease off |
| Swollen feet and ankles | Fluid retention | Feet up; report sudden swelling |
| Shortness of breath | Uterus pressing on the diaphragm | Sit upright; urgent help if severe or with chest pain |
| Needing to pee more | Baby's head on your bladder | Cut down on drinks before bed, not overall |
| Leg cramps | Not fully understood | Calf stretches; see pregnancy leg cramps |
Sleep on your side. The NHS says research suggests that after 28 weeks, falling asleep on your back can double the risk of stillbirth. Go to sleep on your left or right side; if you wake on your back, just turn over.
Your baby's movements and kick counting
From 28 weeks, knowing your baby's normal pattern matters. The NHS says there's no set number of movements, and you should feel your baby move right up to and during labor. What matters is a change.
- Get to know your baby's usual pattern of kicks, rolls and jabs.
- If movements slow down, stop or change, call your maternity unit immediately. Don't wait until the next day.
- Don't use a home doppler to check, and don't try to make your baby move first.
Some providers suggest a daily count-to-10. Read kick counts: how and when or use the kick counter.
Appointments in the third trimester
Checks usually include your blood pressure, urine, the size of your bump and your baby's position and heartbeat. Some people are offered a growth scan. ACOG notes induction may be recommended if you reach 41 weeks. See the pregnancy appointment schedule.
Signs of labor
The NHS lists these signs that labor might be starting:
- contractions or tightenings that get longer, stronger and closer together
- a "show", when the mucus plug comes away
- backache
- an urge to go to the toilet
- your waters breaking
The NHS advises calling your midwife or maternity unit if you think you're in labor or have regular contractions every 5 minutes or more often. Call urgently if your waters break, you have bleeding, your baby is moving less, you're under 37 weeks and think you're in labor, or contractions last longer than 2 minutes or come 6 or more times in 10 minutes. Time yours with the contraction timer and read how to time contractions.
Warning signs to act on
Call your provider or maternity unit straight away for:
- reduced or changed movements
- vaginal bleeding or fluid leaking
- a severe headache, problems with your vision, pain under your ribs, or sudden swelling of your face, hands or feet (possible pre-eclampsia)
- regular contractions or pressure before 37 weeks
- fever, or feeling very unwell
How Momi helps
In the third trimester, Momi gives you a one-tap kick counter (sessions saved, with a goal of 10) and a contraction timer that logs length and time between contractions, with averages. You'll still see your weekly baby size, weeks to go and tips, plus visits with medicine reminders and your bump photo journal.
Download Momi free on the App Store or Google Play. Free with ads; optional Premium.
Sources
- ACOG, How Your Fetus Grows During Pregnancy
- Mayo Clinic, Fetal development: The 3rd trimester
- NHS, Your baby's movements
- NHS, Signs that labour has begun
- NHS, Tiredness and sleep problems
- ACOG, Committee Opinion 579: Definition of Term Pregnancy
- NHS, Pre-eclampsia
Medical disclaimer: Momi and this website provide general information, not medical advice. Always talk to your doctor or midwife; in an emergency call your local emergency number.
FAQ
Does the third trimester start at 27 or 28 weeks?
At 28 weeks. Both ACOG and the NHS put week 27 at the end of the second trimester, with the third trimester starting at 28 weeks 0 days. Some websites round differently, which is why you may see 27 weeks mentioned.
How many months is the third trimester?
Roughly months 7 to 9. It runs from 28 weeks until birth, which is about 12 to 14 weeks for most people, so it's often a little longer than three calendar months, especially if your baby arrives after the due date.
What are the warning signs in the third trimester?
Call your maternity unit straight away if your baby moves less or the pattern changes, you have bleeding, your waters break, regular contractions before 37 weeks, or a severe headache, vision problems or sudden swelling of your face, hands or feet, which can be signs of pre-eclampsia.
How often are appointments in the third trimester?
More often than before. In the US, visits are often every 2 weeks from about 28 weeks and weekly from 36 weeks. In England, a first pregnancy usually has appointments at 28, 31, 34, 36, 38 and 40 weeks. Your schedule depends on your needs.
What is considered full term?
ACOG calls 37 to 38 weeks 6 days early term, 39 to 40 weeks 6 days full term, 41 weeks late term and 42 weeks or more post-term. A baby born before 37 weeks is preterm.
Related guides
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