39 weeks pregnant

How big is your baby at 39 weeks?

About the size of a small watermelon — around 50.7 cm (20.0 in) head to heel. The almost-transparent skin of a few weeks ago now has a tougher outer layer, better at protecting the organs underneath and at holding a temperature.

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).

What's developing this week

The skin is coated in vernix — Latin for varnish — the creamy white layer that protects it in the amniotic fluid and eases the journey down the birth canal. Some babies are born covered in it; on others it has mostly gone. Neither means anything.

The NHS also uses this week to set expectations for the first minutes after birth, worth reading now rather than in the moment: babies do not usually come out wailing, and it can take a few seconds before they cry or splutter their airways clear. Hands and feet can look blue while the circulation catches up. And it is not always love at first sight — give yourself time, and ask for help if you need it.

What you might feel

Discharge increases — thin, white, not smelling of much. A slimy blob of mucus that is yellow or bloody is a show, the plug that sealed your cervix coming away. It can be one of the first signs labour is on the way, and the NHS is quick to add that you could still have days to wait. If you are losing more blood than that, phone straight away.

Back pain as your baby presses on your spine, increased pressure low in your bump, sudden bursts of nesting energy, and practice contractions that are starting to be less easy to describe as practice.

Movements do not slow down at the end

A show, a twinge and a packed bag do not change this instruction by one word. 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 39 weeks pregnant 9 months or 10 months?

Week 39 is in month 9, its fourth week. There is no month 10 on the standard mapping: 40 weeks is a little over nine calendar months, which is why the two counts never quite line up.

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 no routine NHS appointment at 39 weeks — the next is at 40. But something specific starts being offered from this week: NICE asks that at antenatal visits after 39+0 weeks, your midwife or doctor discusses whether you would like a vaginal examination for membrane sweeping, and obtains your verbal consent before doing one.

A sweep is a gloved finger swept around the cervix to separate the membranes from it, releasing prostaglandins that may start labour. Tommy's says it might bring on labour within 48 hours without a medical induction, that it is usually uncomfortable rather than painful, and that cramping and light bleeding afterwards are normal. There is a small chance it breaks your waters. Tommy's also makes a point about consent worth holding on to: you should not be asked to agree to a sweep while an internal examination is already happening, because you need time to think about it first.

39 weeks is where "full term" starts — and where the countries part

On the ACOG labels, full term begins at 39+0 and runs to 40+6. That is the window in which adverse neonatal outcomes are lowest, and the reason ACOG says elective induction should not be done before 39 weeks when a woman and her baby are healthy.

From 39 weeks, though, the two systems genuinely diverge, and if you have read American and British advice side by side this is what confused you:

• United States. ACOG has a dedicated FAQ on induction at 39 weeks. It says research suggests induction for healthy women at 39 weeks in a first full-term pregnancy may reduce the risk of caesarean birth, and that those women may also have lower rates of pre-eclampsia and gestational hypertension. The criteria it names are: a first full-term pregnancy, one baby, and both of you healthy. It also notes that whether it is available depends on whether your hospital has the staff and resources.
• United Kingdom. NICE does not offer routine induction at 39 weeks. Its position is to give uncomplicated pregnancies every opportunity to go into spontaneous labour, and it frames the induction discussion from 41+0 weeks. The NHS offers induction if labour has not started naturally by 41 weeks.

Neither body is wrong and neither is quoting the other's evidence badly. If you are being offered something at 39 weeks that your friend in another country was not, this is why.

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.