21st week: The sixth month begins

Weeks and days
20+0 to 20+6
Month
6
Trimester
2

The 6th month of pregnancy begins with the 21st week of pregnancy. This week, the fetus grows from about 166 to 179 millimeters and weighs around 400 grams by the end. It is now forming brown fat, which keeps it warm after birth.

A single large eggplant lies in an open palm on beige linen
Eggplant200 to 250 mm, the size of your baby at the end of the week

Week 21 of 40

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How big is the fetus?

050100150200250 mm19th week142 to 15320th week153 to 16621st week166 to 17922nd week179 to 191Eggplant at the same scale

166 to 179 mm

By the end of the week, the fetus is about the size of an eggplant. From head to heel, it measures about 26 centimeters.

Crown-rump length at the transition from the UNSW Embryology table to the values from Archie et al. 2006, weight according to the WHO growth charts. A large eggplant is 200 to 250 mm long.

This week

Your baby

  • Brown fat is forming. After birth, it produces heat.
  • Movements and breathing movements follow a daily rhythm: in one study, they were least frequent in the morning and most frequent in the evening.
  • Antibodies from your blood can pass through the placenta to the baby.

Your body

  • The distance from the pubic bone to the top of the uterus is on average 21 cm by the end of the week.
  • If your baby is especially active in the evening, that is normal. Many feel it just when they want to sleep.
  • Swollen feet are common. If severe swelling suddenly appears in the face and hands after the 20th week of pregnancy, it can be a sign of preeclampsia.

What matters now

  • In Germany, the second basic ultrasound is still possible until 21+6.
  • From the 6th month, the hemoglobin level is, as a rule, also measured at prenatal checkups in Germany.
  • A resting blood pressure of 140/90 mmHg or higher is considered high. About 2 out of 100 pregnant women in Europe develop preeclampsia, usually after the 20th week.

Get checked right away: heavy bleeding, severe or persistent abdominal pain, fever, pain when urinating, or vomiting where you cannot keep anything down.

Gestational sacPlacentaFetus with heartbeat

On ultrasound

  1. 20+0

    Head circumference is on average about 173 mm.

  2. 20+0

    Abdominal circumference measures on average about 150 mm.

  3. 20+0

    Thigh bone (femur) measures on average about 32 mm.

The ultrasound now estimates the weight from the head, abdomen, and thigh bone. The length from crown to rump is no longer measured.

Frequently asked questions about the 21st week of pregnancy

Which month is the 21st week of pregnancy?

The first week of the 6th month of pregnancy, in the 2nd trimester. Figures such as 20+3 weeks also belong to the 21st week of pregnancy.

Is it normal for the baby to hardly move in the 21st week of pregnancy?

Yes. With a first child, many only feel the movements after the 20th week, and even after that there are breaks of several minutes. If you have not felt anything by the 24th week, let your midwife or doctor know.

Why do I feel sick again in the 21st week of pregnancy?

For most, the nausea is over by now: in one study, 90 out of 100 women were free of symptoms by the 22nd week. If new nausea comes with upper abdominal pain or headaches and swelling, have it checked by a doctor.

Can a baby survive in the 21st week of pregnancy?

Not outside the womb. The German guideline sees no realistic chance before 22+0.

Sources

Updated on 30 October 2026 · Fertilio Editorial Team