Illustration of a baby at week 40 inside the womb in cross-section, with the placenta and umbilical cord — Womb in cross-section, enlarged to show detail. Not true size. Most babies are head-down by about 36 weeks.

Third trimester, week 40

40 weeks pregnant: Due date!

Size of a: Watermelon
Length: 51.2 cm head to heel
Weight: 3.6 kg WHO median
Heart rate: 110–160 bpm typical range
Due date: This week 100% of the way

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Checked against the sources listed on this page. Not reviewed by a clinician. Last updated 5 November 2026. How we check.

At 40 weeks pregnant, your baby is about the size of a watermelon: roughly 51.2 cm from head to heel, weighing about 3.6 kg. You’re in your third trimester, and this is the week of your due date.

Your baby this week

The average newborn is about 51 cm long and weighs about 3.5 kg, but anything from roughly 2.5 kg to 4 kg is common.
The baby is fully ready to breathe, feed and regulate temperature, with your help.
Newborns recognise your voice and smell and prefer faces to other shapes.

Your body this week

If labour hasn’t started, you’ll be offered monitoring and a plan. Induction is usually offered between 41 and 42 weeks.
Waiting can feel long, so keep up gentle activity and rest.
After birth, skin-to-skin contact helps regulate the baby’s temperature, heart rate and blood sugar.

Typical weight gain so far: 11.6–16 kg
Your uterus: Near the ribs, may drop as baby engages

Weight gain range is for a pre-pregnancy BMI of 18.5–24.9 (IOM guideline). Your provider may advise differently.

What happens if you go past 40 weeks

Your due date is an estimate, and going past it is common, especially with a first baby. In the UK you’ll have an appointment at 40 weeks and another at 41 weeks, to check your blood pressure, urine, bump and the baby’s position, and to talk through your choices.

Membrane sweep: what it is

A membrane sweep may be offered before induction, usually after 39 weeks. During an internal examination, a midwife or doctor sweeps a finger around your cervix to help start labour. It can cause some cramping or light bleeding. If labour doesn’t start, you may be offered another sweep or induction. Read the full membrane sweep guide.

When is labour induced?

The NHS offers induction if labour hasn’t started by 41 weeks, because the risk of stillbirth or other problems for the baby becomes higher. It may be offered earlier for reasons such as diabetes, high blood pressure or cholestasis, or if your waters broke more than 24 hours ago and labour hasn’t begun. Timing varies between countries and hospitals. ACOG says induction may be recommended if a pregnancy reaches 41 weeks. In the US, 41 to 42 weeks is called late term, and beyond 42 weeks is postterm.

It’s your choice. If you go past 42 weeks and decide against induction, you should be offered increased monitoring of you and your baby.

Keep watching movements at 40 weeks

Your baby should keep moving in their usual pattern right up to and during labour. If movements slow down, stop or change, call your maternity unit immediately, even at night.

Scans, tests and checkups

This week

Know your baby’s movements Self-care
Get to know your baby’s pattern. If movements slow down, change or stop, contact your maternity unit straight away. Don’t wait until the next day.
This week

Weekly checkups Checkup
Blood pressure, urine, growth, position and movements, plus planning for labour. Often weekly in the US. The NHS schedule is usually 36, 38 and 40 weeks.
This week

Membrane sweep & post-dates plan Checkup
A membrane sweep may be offered. If labour doesn’t start, induction is usually offered between 41 and 42 weeks.

See the full scan and test timeline

Real size, next to an adult hand

Adult hand 18.5 cmbaby 34.8 cm curled up

Growth curve

Typical weight by week: WHO median from week 20, approximate before that. Healthy babies vary widely.

When to call your midwife or doctor at 40 weeks

Call your midwife, doctor or maternity unit straight away, day or night, if you have any of these:

A change in your baby’s usual pattern of movement. Call straight away rather than waiting until the next day.
Vaginal bleeding, or a gush or steady trickle of fluid.
Severe belly pain that doesn’t go away.
A severe headache, vision changes, pain under your ribs, or sudden swelling of your face, hands or feet. These can be signs of pre-eclampsia.
Regular, strong contractions or your waters breaking. Follow what your maternity team told you about when to come in.
Intense itching, especially on your hands and feet, which can be a sign of a liver condition called cholestasis.
Fever of 38 °C (100.4 °F) or higher, or pain or burning when you pee.
Pain or swelling in one leg, chest pain, or sudden shortness of breath. These can be signs of a blood clot.
Feeling very low, hopeless or anxious most days. If you feel you might harm yourself, get emergency help.

Based on NHS and ACOG guidance. This list isn’t complete. If something feels wrong, call anyway. In an emergency, call your local emergency number.

Tip for this week

If you go past your due date, keep an eye on movements and know when your next check is. Most people go into labour on their own by 42 weeks.

Myth or fact?

Will my baby be born on the due date?

Myth

Unlikely. Only about 4% of babies arrive on their exact due date. Most are born within about two weeks either side.

Read the evidence

Common questions at this stage

All common questions

More myths around week 40

Is pregnancy really 9 months? Partly true

Questions people ask about week 40

What happens if I go past 40 weeks?

You’ll usually be offered extra checks and a membrane sweep, and induction is typically offered between 41 and 42 weeks, depending on your situation and local guidelines.

How big is a baby at 40 weeks?

On average about 51 cm long and around 3.5 kg. Healthy newborns commonly range from about 2.5 kg to 4 kg or more.

References

Advice differs between countries, so follow your own care team’s plan. Weights from week 20 are the WHO median, and earlier weights are approximate. How we check this.