40 weeks pregnant: development, labour and when to call
40 weeks pregnant is the week the NHS says the wait is nearly over, with the baby around 51.2 cm long from head to heel, about the size of a pumpkin (NHS, 2026). This page sets out what the NHS, ACOG and the Office on Women’s Health say about week 40, including the stages of labour and when to call.
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Medically reviewed by Dr Mary Davidson, Reproductive endocrinologist, checked on
Seek help now if you have any of these symptoms
Bleeding and cramping are common in early pregnancy and often do not mean miscarriage. The symptoms below, however, need to be assessed straight away.
- Soaking two or more sanitary pads per hour, or passing large clots
- Severe lower abdominal pain, especially on one side
- Pain at the tip of the shoulder
- Dizziness, fainting, or collapse
- Signs of shock — pale, clammy, rapid heartbeat, breathlessness
- Pain on opening bowels, or bladder or bowel changes
- Feeling very unwell, or feverish
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How the sources describe development around 40 weeks
- Size and shape, NHS
- The NHS week 40 page in its week-by-week guide (NHS, 2026) gives the baby as around 51.2 cm long from head to heel and compares it to a pumpkin. It says the baby is getting rather squashed up now but should still be moving around in their usual pattern.
- Size at birth, Office on Women’s Health
- The Office on Women’s Health page on the stages of pregnancy (2025) says that at birth a baby may weigh somewhere between 6 pounds 2 ounces and 9 pounds 2 ounces and be 19 to 21 inches long, that most full-term babies fall within these ranges, and that healthy babies come in many sizes.
- Development, ACOG
- ACOG’s list for weeks 37 to 40 includes the circulatory and musculoskeletal systems being done developing, the lungs, brain and nervous system finishing their development, and fat continuing to be added all over to keep the baby warm after birth (ACOG, How Your Fetus Grows During Pregnancy, 2024).
Weeks are counted from the first day of the last menstrual period, so about two weeks of the count come before conception (ACOG, How Your Fetus Grows During Pregnancy, 2024). This page covers 40 weeks 0 days to 40 weeks 6 days.
Movements and contact
The NHS says the baby’s movements should not slow down or stop, and that if you notice any changes you should contact your midwife or maternity unit straight away, adding that someone there will answer calls 24 hours a day (NHS, 2026). NICE guideline NG201 says women should contact maternity services at any time of day or night if they have any concern about the baby’s movements (NICE, 2021).
Your body at 40 weeks, as the NHS describes it
The NHS says that if this is your first baby you will have an antenatal appointment this week, at which your blood pressure is checked, your bump measured and a urine sample taken, and that the midwife or doctor will be checking for signs of pre-eclampsia. It says you are probably getting a lot of practice contractions now, called Braxton Hicks contractions, which should not be painful, and that real contractions hurt when your bump goes tight and the pain goes away when the muscles relax (NHS, 2026).
The stages of labour, as the NHS describes them
The NHS says labour has three stages. In the first, you have contractions and your cervix opens up until it is 10 cm across, which it says lasts 6 to 12 hours, or less if you have had other children. In the second, the baby is delivered. In the third, the placenta comes out (NHS, 2026). The NHS says that when your contractions last at least 60 seconds and come every 5 minutes you should call your hospital or midwife (NHS, 2026). The box above lists symptoms that need urgent help at any time.
Bringing on labour
The NHS says there are no proven ways to safely bring on labour at home, and that you should get advice from your doctor or midwife before trying anything other than watching and waiting (NHS, 2026). NICE says care teams should discuss prolonged pregnancy and how to manage it from 38 weeks (NICE, 2021).
How the week is counted
ACOG says a normal pregnancy lasts about 40 weeks from the first day of the last menstrual period, and defines the third trimester as 28 weeks 0 days to 40 weeks 6 days (ACOG, 2024).
Work out which week you are in
The Pregnancy week calculator takes your last period, conception date, scan or IVF transfer and shows how many weeks and days pregnant you are today.
Sources
- NHS Best Start in Life. Week 40 of pregnancy (week-by-week guide to pregnancy). nhs.uk, 2026.
- National Institute for Health and Care Excellence. Antenatal care (NG201). NICE, 2021.
- American College of Obstetricians and Gynecologists. How Your Fetus Grows During Pregnancy (FAQ156). ACOG, 2024.
- Office on Women's Health, US Department of Health and Human Services. Stages of pregnancy. womenshealth.gov, 2025.
Frequently asked questions
What are the stages of labour?
The NHS says the first stage is contractions while the cervix opens to 10 cm, lasting 6 to 12 hours or less if you have had other children, the second is the delivery of the baby, and the third is the delivery of the placenta (NHS, 2026).
When should I call the hospital or midwife at 40 weeks?
The NHS says to call your hospital or midwife when your contractions last at least 60 seconds and come every 5 minutes, and to contact your midwife or maternity unit straight away if the baby’s movements slow down or stop (NHS, 2026). The box above lists symptoms that need urgent help.