40th week: Three and a half kilograms

Weeks and days
39+0 to 39+6
Month
10
Trimester
3

In the last week before the due date, the fetus gains from about 3,400 to 3,620 grams and, on average, passes three and a half kilograms. The calculated due date, 40+0, is the day after this week. Only about one in twenty babies is born on exactly that day.

Side view of a round baby bump in the 40th week of pregnancy, the hands resting beneath the bump, warm window light
around 3.6 kghow heavy your baby is at the end of the week

Week 40 of 40

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How big and how heavy is the fetus?

050100150200250300350400 mm38th week327 to 33639th week336 to 34440th week344 to 35241st week352 to 360

344 to 352 mm

By the end of the week, the fetus weighs about 3,620 grams. From head to heel, it measures about 49 centimeters.

Crown-rump length according to the values from Archie et al. 2006, weight according to the WHO growth charts.

This week

Your baby

  • A few weeks ago, the skin was almost see-through. Now a firmer layer is forming.
  • A white, waxy layer, the vernix, covers the skin. It protects against heat loss and eases the way through the birth canal.
  • The fingernails extend beyond the fingertips. In boys, the testicles are in the scrotum or can be felt in the groin.

Your body

  • More discharge is normal. It should be thin and white and have hardly any smell.
  • When the baby slips deeper into the pelvis, it presses against your spine. Back pain and downward pressure increase.
  • The uterus is now one to two finger widths below the lower edge of your ribs.

What matters now

  • Call the hospital or your midwife when contractions last at least 60 seconds and come every 5 minutes. If there is bleeding or the baby stops moving, call right away.
  • In Germany, prenatal checkups take place every two weeks until the due date. Once it has passed, you are examined more often.
  • If the baby comes later, maternity protection before the birth is extended accordingly in Germany and Austria. In Switzerland, maternity compensation begins on the day of the birth.

Get checked right away: bleeding from the vagina, greenish or foul-smelling amniotic fluid, fewer baby movements than usual, a contraction that lasts longer than 2 minutes, severe headache, vision problems, or severe swelling of the face, hands, and feet.

Gestational sacPlacentaFetus with heartbeat

On ultrasound

  1. 39+0

    Head circumference is on average about 337 mm.

  2. 39+0

    Abdominal circumference measures on average about 350 mm.

  3. 39+0

    Thigh bone (femur) measures on average about 73 mm.

In Germany, Austria, and Switzerland, no routine ultrasound is scheduled.

Frequently asked questions about the 40th week of pregnancy

How likely is a birth on the calculated due date?

Low. Only about 5 out of 100 babies are born exactly on the due date. In a large study, half of spontaneous births took place before and half after day 283 after the last period, that is, 40+3.

I have lower abdominal pain but no contractions. What does that mean?

This can be the start of labor, the latent phase. The cervix becomes soft and thin and begins to open. This can take hours, sometimes even days.

What is a membrane sweep?

A doctor or midwife uses one or two fingers to separate the membranes in the lower part of the uterus. This stimulates the body to release hormones that promote contractions. Two membrane sweeps within one week work more often than one. In the UK, it is offered from 39+0.

My water has broken. When do I need to go to the hospital?

Call your midwife or the labor ward and set off. Contractions usually start within 24 hours. Otherwise, an induction is recommended at that point at the latest, because the risk of infection rises.

Sources

Updated on 31 October 2026 · Fertilio Editorial Team