Third trimester: how many weeks, and what happens
By Pregora Editorial Team · Updated 2026-08-25 · 9 min read
The third trimester starts at 28 weeks and 0 days and runs until birth. If your baby arrives on the estimated date that is about thirteen weeks, though the finish line moves, which is rather the point of this stage.
It is also the trimester where the week number starts to carry real weight. In the first two, weeks mostly mark development. Here they determine what happens if labour begins.
What each week actually means
These are gestational weeks, counted from your last period.
- 28 weeks. The trimester begins. Appointments become more frequent. If you are rhesus negative, anti-D is usually given around now. This is also when movement monitoring matters most.
- 32 weeks. A growth scan for some pregnancies, depending on risk factors and local policy.
- 34 weeks. Appointments often move to fortnightly, then weekly. Birth preferences are usually discussed around here.
- 36 weeks. Position is checked. Most babies are head-down by now, and where one is breech, turning it manually may be offered from about 36 to 37 weeks. Group B strep screening happens in this window in countries that screen routinely.
- 37 weeks. Early term. No longer classed as premature.
- 39 weeks. Full term.
- 41 weeks. Late term. Induction is usually being discussed by now.
- 42 weeks. Post term. Very few pregnancies are allowed to continue past this.
Why 37 weeks is not "full term"
This one causes genuine confusion, because 37 weeks was described as full term for decades and plenty of people still use it that way.
The definitions were tightened because outcomes at 37 and 38 weeks were found to differ measurably from outcomes at 39 and 40. Babies born in that earlier window had slightly higher rates of breathing difficulty and feeding problems. So the single label was split into four:
| Term | Weeks |
|---|---|
| Early term | 37 weeks 0 days to 38 weeks 6 days |
| Full term | 39 weeks 0 days to 40 weeks 6 days |
| Late term | 41 weeks 0 days to 41 weeks 6 days |
| Post term | 42 weeks 0 days and beyond |
In practice this is why elective procedures are not usually scheduled before 39 weeks without a medical reason. Those two extra weeks turn out to be worth something.
The trimester calculator shows which trimester you are in and how many days are left in it. For the term milestones above, the due date calculator gives the exact dates you will hit 37, 39 and 41 weeks.
Movement is the thing to watch
Of everything in this trimester, fetal movement is the one signal worth treating as non-negotiable.
The old advice about counting to ten kicks has largely been replaced by something simpler and more useful: learn your own baby's pattern, and report any change from it. There is no set number of movements that is normal, because babies differ enormously.
Two myths worth putting down. Babies do not move less towards the end because they have run out of room. And movement does not reliably slow down before labour. If movements reduce or the pattern changes, that needs assessing the same day, whatever week you are in and however well you feel otherwise.
Ring your maternity unit straight away for: reduced or changed movements, any bleeding, waters breaking, contractions before 37 weeks, a severe headache with visual disturbance or pain under your ribs, or sudden swelling of the face and hands. The last group are signs of pre-eclampsia, which is why blood pressure and urine are checked at every appointment in this trimester.
What tends to be hardest
The physical complaints of this trimester are mostly mechanical. The uterus is now large enough to press on things.
Heartburn comes from pressure on the stomach combined with a relaxed valve at its entrance. Breathlessness comes from reduced room for the diaphragm, and often eases once the baby drops. Needing to urinate constantly returns for the same reason it did in the first trimester, this time from direct pressure rather than hormones. Back and pelvic pain come from ligaments softening and the centre of gravity shifting.
Sleep is frequently the worst of it, and it is a genuinely awkward combination: heartburn, needing the bathroom, a body that no longer has a comfortable position, and a baby who is often most active at night.
Weight gain typically settles at around a pound a week through this stretch, which we cover against the IOM ranges in pregnancy weight gain by trimester.
Frequently asked questions
How many weeks is the third trimester?
It begins at 28 weeks 0 days and ends at birth. On the estimated due date that is about thirteen weeks, but the actual length depends entirely on when labour starts.
What happens at 36 weeks?
Position is checked, since most babies are head-down by now. If yours is breech, turning it manually may be offered from around 36 to 37 weeks. Group B strep swabs are taken in this window where routine screening is offered, and appointments usually become weekly.
Is 37 weeks full term?
No. 37 weeks is early term. Full term is 39 weeks 0 days to 40 weeks 6 days. The distinction exists because outcomes at 37 and 38 weeks differ slightly from those at 39 and 40, and it is why elective procedures are generally not scheduled before 39 weeks without a reason.
Do babies move less near the end?
No. The character of the movements changes as space reduces, so rolls and pushes replace sharp kicks, but the frequency should not drop. Any reduction needs reporting the same day. This is one of the most commonly repeated pieces of misinformation in late pregnancy.
Disclaimer: General education, not medical advice. Appointment schedules, screening offered and induction policy vary by country and by provider. Your own midwife or obstetrician is the authority on your care.