Illustration of a baby at week 21 inside the womb in cross-section, with the placenta and umbilical cord — Womb in cross-section, enlarged to show detail. Not true size.

Second trimester, week 21

21 weeks pregnant: Kicks you can feel

Size of a: Carrot
Length: 26.7 cm head to heel
Weight: 398 g WHO median
Heart rate: 110–160 bpm typical range
Due date: 133 days away 53% 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 21 weeks pregnant, your baby is about the size of a carrot: roughly 26.7 cm from head to heel, weighing about 398 g. You’re in your second trimester, with about 19 weeks to go until your due date.

Your baby this week

Movements are stronger and more coordinated. The baby kicks, rolls and punches.
Bone marrow is starting to help the liver and spleen make blood cells.
Eyebrows and eyelids are fully formed.

Your body this week

Braxton Hicks contractions, painless tightenings of the belly, may begin. They are practice, not labour.
Swollen ankles and feet, especially later in the day, are common.
Varicose veins can appear in the legs or vulva because of increased blood volume and pressure.

Typical weight gain so far: 3.8–6.2 kg
Your uterus: Around your belly button

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

Scans, tests and checkups

This week

Second-trimester (quad) screening Blood test
A blood test (AFP, hCG, estriol, inhibin-A) for chromosomal conditions and neural tube defects, if you didn’t have first-trimester screening or NIPT. The NHS offers it at 14–20 weeks.
This week

Anatomy scan (anomaly scan) Ultrasound
A detailed ultrasound of the baby’s brain, heart, spine, face, kidneys, limbs and growth, plus the placenta position and fluid. The NHS usually does it at 18–21 weeks.

Baby’s sex: Sex usually visible if the baby’s position allows. Ask if your hospital reports it
From week 24

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.
From week 24

Glucose test (gestational diabetes) Blood test
A sugary drink followed by blood sugar checks. The UK offers it based on risk factors. The US screens almost everyone.

See the full scan and test timeline

Real size, next to an adult hand

Adult hand 18.5 cmbaby 18.2 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 21 weeks

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

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 tightenings, period-like cramps or lower back pressure that keep coming. This could be early labour.
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

Put your feet up when you can, avoid standing still for long periods, and consider compression stockings for swelling.

Common questions at this stage

All common questions

Questions people ask about week 21

What do Braxton Hicks feel like?

A tightening or hardening of the belly for about 30 seconds to 2 minutes, usually irregular and painless. Regular, painful contractions before 37 weeks should be checked urgently.

How much should the baby move at 21 weeks?

Movements are becoming more noticeable but aren’t yet a set pattern. From about 24–28 weeks, get to know your baby’s pattern and report any reduction.

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.