21 weeks pregnant: development, hearing and staying steady
21 weeks pregnant is a stage at which, the NHS says, the baby is around 26.7 cm long from head to toe, about the size of a carrot, and can hear noises and voices outside the womb (NHS, 2026). This page sets out what the NHS and ACOG say about week 21.
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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 21 weeks
- Size and shape, NHS
- The NHS week 21 page in its week-by-week guide (NHS, 2026) gives the baby as around 26.7 cm long from head to toe and compares it to a carrot. It says the baby is now heavier than the placenta, and is developing a fine downy layer of hair called lanugo, and hair and eyebrows.
- Senses and movement, NHS
- The NHS says the baby can now hear noises and voices outside the womb, is moving around a lot and is establishing waking and sleeping patterns. It says the baby is getting ready for life outside the womb and developing essential skills including sucking and breathing (NHS, 2026).
- Development, ACOG
- ACOG groups weeks 21 to 24 together. Its list includes kicks and turns getting stronger, the sucking reflex developing, fat forming under the skin, and ridges forming in the hands and feet that later become fingerprints and footprints (ACOG, How Your Fetus Grows During Pregnancy, 2024). The list is not broken down week by week.
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 21 weeks 0 days to 21 weeks 6 days.
A normal pregnancy lasts about 40 weeks from the first day of the last menstrual period, so at 21 weeks about 19 weeks remain to the estimated due date (ACOG, How Your Fetus Grows During Pregnancy, 2024). Your own due date depends on your last period or a scan, not on the week alone.
Your body at 21 weeks, as the NHS describes it
The NHS says you may start to feel a little unsteady as your bump gets bigger, because your centre of gravity has changed and your joints are looser. It says that if you have a tumble you should try not to panic, as the baby is well protected, but that you should let your midwife know as soon as possible (NHS, 2026).
The NHS also says the baby may be wide awake when you are ready to sleep, and that napping when you can may make up for lost sleep at night (NHS, 2026).
Whooping cough vaccination
The NHS says the whooping cough vaccine is usually offered to pregnant women around week 20 but can be had from week 16 to week 32, and that if you have not had it yet you should speak to your midwife or GP (NHS, 2026).
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 21 of pregnancy (week-by-week guide to pregnancy). nhs.uk, 2026.
- American College of Obstetricians and Gynecologists. How Your Fetus Grows During Pregnancy (FAQ156). ACOG, 2024.
Frequently asked questions
Can the baby hear at 21 weeks pregnant?
The NHS says the baby can now hear noises and voices outside the womb (NHS, 2026). Its week 15 page says hearing starts around then, and ACOG lists hearing as starting to develop in weeks 13 to 16 (ACOG, 2024). The sources describe hearing developing over several weeks.
What should I do if I fall over at 21 weeks?
The NHS says to try not to panic, as the baby is well protected, but to let your midwife know as soon as possible (NHS, 2026). The box above lists the symptoms that need urgent help.