40 weeks pregnant

How big is your baby at 40 weeks?

About the size of a pumpkin — around 51.2 cm (20.2 in) head to heel, the last weekly length the NHS publishes.

A note on the numbers: these are head-to-heel lengths. The NHS gives one for every week of the third trimester but no weekly weight — the only weight it publishes in this range is at 41 weeks, where the average baby is around 3 to 4 kg (6 lb 10 oz to 8 lb 13 oz). Your baby is thoroughly squashed by now but should still be moving in their usual pattern. The NHS puts it in the plainest terms it uses anywhere: movements should not slow down or stop, and if they do, it could be an important sign that something is wrong.

What's developing this week

Very little that is new, which is the definition of the week. Your baby is putting on the last of the fat that will regulate their temperature, and practising the breathing movements that will become breathing.

What you might feel

The NHS offers an unusually recognisable description of early labour: feeling as though you have PMT, or having lower backache. Alongside that, a lot of Braxton Hicks, which should not be painful. When real contractions start, the NHS says, you will know about it — the pain comes as your bump goes tight and goes away as the muscles relax.

Be on alert for your waters breaking, which can happen at any time. Do not expect a tidal wave; it can be a trickle. If you think it has started, call. You might simply have wet yourself — nobody minds — but if your waters have broken, labour may need to be induced because of the infection risk.

Movements do not slow down at the end

This is the week people talk themselves out of ringing because they assume labour is imminent anyway. Ring. Call your midwife or maternity unit immediately if your baby is moving less than usual, if you cannot feel them moving, or if their usual pattern has changed — do not wait until the next day, do not wait for your next appointment, and call even in the middle of the night. Those are the NHS's own words, and maternity triage is staffed 24 hours a day for exactly this call.

Babies do not move less at the end because they have run out of room. The RCOG says movements tend to increase until about 32 weeks then stay roughly the same, and that you should feel your baby move right up to and during labour. Nor do you need to count: the NHS says "you do not need to count the number of kicks or movements you feel each day", and RCOG Green-top Guideline No. 57, second edition, reviewed 29 April 2026, found insufficient evidence to recommend counting using specified numbers. What matters is a change from your baby's own pattern.

Tommy's reports that 55% of women who had a stillbirth had noticed their baby's movements slow down or stop and had not reported it. Our movements counter records what normal looks like for your baby, but no number on it means everything is fine — and a home Doppler is worse: the NHS says hearing a heartbeat does not mean your baby is well.

Is 40 weeks pregnant 9 months or 10 months?

Week 40 is the last week of month 9. Forty weeks is a little over nine calendar months, never ten, which is exactly the arithmetic that makes "nine months pregnant" feel like it should already be over.

There is no official weeks-to-months map, and a calendar month averages 4.3 weeks rather than 4, so 40 weeks is a little over nine months. The usual mapping:

• Month 1 — weeks 1 to 4
• Month 2 — weeks 5 to 8
• Month 3 — weeks 9 to 13
• Month 4 — weeks 14 to 17
• Month 5 — weeks 18 to 22
• Month 6 — weeks 23 to 27
• Month 7 — weeks 28 to 31
• Month 8 — weeks 32 to 35
• Month 9 — weeks 36 to 40

Your maternity team counts in weeks and days. Our weeks to months converter shows both mappings.

What's happening at your appointments around now

There is a 40-week appointment on the NHS schedule; the week-by-week guide notes it applies if this is your first baby. Your blood pressure is checked, your bump measured and a urine sample taken, specifically looking for the signs of pre-eclampsia that you would not notice yourself. Your midwife will feel for your baby's position, discuss movements and your mental health, and discuss your choices if you are still pregnant after 40 weeks.

If a membrane sweep has not already been mentioned, it can be now — NICE asks that it is discussed and separately consented to at visits after 39+0.

Only about 4 in 100 babies arrive on the due date

Tommy's puts it exactly that way: "Only around 4 in 100 babies are born on their due date as it is just an estimate." Your due date is the day your pregnancy reaches 40 weeks, calculated by adding 280 days to the first day of your last period and then usually corrected by your dating scan. It was always a midpoint, not an appointment.

NICE publishes the real distribution, from NHS maternity data, of when spontaneous labours start:

• By the end of week 37 — 12.8% have started
• By the end of week 38 — 24.9%
• By the end of week 39 — 50.3%
• By the end of week 40 — 82.8%
• By the end of week 41 — 99.0%
• 42+0 weeks and over — the remaining 0.9%

Half of everyone is still pregnant at the start of week 40, and roughly a third of all spontaneous labours begin during this week alone. ACOG's version of the same fact: the average pregnancy is 280 days, and most women give birth between 38 and 41 weeks.

Nothing you can do at home reliably brings on labour

The NHS is flat about it: "There are no proven ways of starting your labour yourself at home." Hot baths, particular foods and drinks, sex, herbal supplements — no evidence any of them work, and no safety information at all for herbal supplements. Sex will not cause harm, but avoid it if your waters have broken.

Tommy's is more nuanced. Walking: a small amount of evidence that 30 minutes three times a week may help, and it helps sleep and mood regardless. Dates: some evidence, bigger studies needed. Raspberry leaf tea: experts are unsure whether it works or how safe it is, and there is a long list of situations where you should not take it, including a caesarean in the last two years, high blood pressure or pre-eclampsia, previous premature or very fast labour, placenta praevia, twins or a breech baby. Acupuncture: little to suggest it triggers labour.

If you are timing what you have got, our contraction timer measures start to start and reports the NHS, ACOG and Australian triggers separately, because 5-1-1 is a United States convention and the NHS threshold fires earlier.

When to call your midwife or doctor

These do not wait until morning.

Emergency now: 999 in the UK and Ireland, 911 in the US and Canada, 000 in Australia, 111 in New Zealand

• You think your baby is coming now and you have a strong urge to push
• You have a seizure, or you collapse

Call your midwife or maternity unit immediately, whatever the hour

• Your baby is moving less than usual, or the pattern has changed
• Your waters break — and again if the fluid is smelly, green or bloodstained
• Any vaginal bleeding
• Any contraction lasting longer than 2 minutes, or 6 or more contractions in every 10 minutes
• A severe headache painkillers do not shift, blurred vision or flashing lights, pain just below the ribs, sudden swelling of your face, hands or feet, vomiting or feeling very unwell — the NHS pre-eclampsia symptoms
• Severe itching at night, a temperature above 37.5C with no cold or flu symptoms, or persistent stomach pain
• You feel that something is wrong, without being able to say what

You do not need to be sure — units would rather see you twice than too late.