DueDate.Baby

21 Weeks Pregnant: Baby Size, Symptoms and UK Milestones

Second Trimester
Guide reviewed: July 2026Reviewed against cited UK guidance

At 21 weeks pregnant, use this UK guide to understand baby size, common symptoms, likely NHS timing, and the practical dates to keep on your radar.

21 weeks pregnant at a glance

  • You are in the second trimester.
  • Your baby is roughly the size of a carrot.
  • Routine midwife appointment to check growth and well-being.
  • Every pregnancy is different, so don't worry if your experience varies slightly.

You are 21 weeks pregnant and in your second trimester. Your baby is about the size of a carrot. This week's key development: Finding a Rhythm. NHS note: Routine midwife appointment to check growth and well-being.

The Anomaly Scan Window

Between 18 and 21 weeks, you'll be offered the anomaly scan. It looks closely at your baby's bones, heart, brain, spinal cord, face, kidneys and abdomen.

20-week scan timing

Estimate the usual anomaly scan window, which is commonly planned around 18 to 21 weeks of pregnancy.

UK maternity leave dates

Use your due date to estimate maternity leave notice, MATB1, and earliest usual leave-start dates.

This page is for general pregnancy planning and date guidance only. It is not medical advice, diagnosis, or treatment. Pregnancy dates are estimates and can change after a scan or advice from your midwife, GP, or maternity team.

If you have symptoms, concerns, or questions about your pregnancy, speak to your midwife, GP, or maternity team. For urgent help, use NHS 111; call 999 in an emergency. Read how we source and review content in our editorial policy.

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Week 20
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Week 22

Baby's Development

Your baby is about the size of a carrot.

Finding a Rhythm — Your baby is establishing sleep and wake cycles, and you may start to notice patterns — active in the evenings, quiet in the mornings, or vice versa. Eyebrows and eyelashes are now visible, and the lips are becoming more defined.

Illustration of a carrot, showing the approximate size of the baby at week 21
Carrot
Approx. 26.7cm

Your Symptoms

  • Varicose veins
  • Stretch marks
  • Increased appetite

Every pregnancy is different. You may experience all, some, or none of these symptoms — and that's completely normal. If anything concerns you, speak to your midwife.

NHS Appointments

Routine midwife appointment to check growth and well-being.

Practical Advice for Week 21

Nutrition

  • Continue vitamin D daily.
  • Eat regular, balanced meals to manage your increased appetite.
  • Include foods rich in vitamin K (broccoli, kale) for blood clotting.
  • Stay well hydrated — 2 litres of water per day is a good target.

Exercise

  • Walking remains one of the best forms of exercise throughout pregnancy.
  • Swimming or aqua aerobics — perfect for supporting your growing body.
  • If varicose veins are appearing, gentle movement helps circulation.
  • Avoid prolonged standing — take regular breaks if your job requires it.

Wellbeing

  • You may notice your baby has sleep and wake patterns — enjoy getting to know them.
  • Stretch marks are common — they affect most pregnant women and fade significantly.
  • Your appetite may increase — eat nutritious foods but don't restrict yourself.
  • If varicose veins are bothering you, support tights can help.

Preparation

  • Routine midwife check — growth and wellbeing assessment.
  • Start assembling a shortlist of baby names.
  • If you're planning a nursery, now is a good time to start (while you have energy).
  • Consider writing a baby shower guest list if friends are planning one.

Tip of the Week

Keep active with walking or swimming to help with circulation and leg aches.

Frequently Asked Questions for Week 21

How many months is 21 weeks pregnant?
At 21 weeks pregnant, you are roughly 4 months pregnant. Remember that pregnancy is typically measured in weeks rather than months for clinical accuracy.
What size is the baby at 21 weeks?
At 21 weeks, your baby is roughly the size of a carrot (about 26.7cm). Your baby is establishing sleep and wake cycles, and you may start to notice patterns
What are the common symptoms at 21 weeks pregnant?
Common symptoms at this stage include varicose veins, stretch marks, increased appetite. Remember that every pregnancy is unique, and it's normal to experience different symptoms.
Is 21 weeks in the second trimester?
Yes, 21 weeks falls within the second trimester.
Are there any NHS appointments at 21 weeks?
Routine midwife appointment to check growth and well-being.

Tools & Calculators

Due Date Calculator UKPregnancy Week CalculatorTimeline by Due DateHow Many Weeks Am I?20-Week Scan CalculatorMaternity Leave Calculator UK

Sources and further reading

Checked for UK week 21 pregnancy information guidance in July 2026.

How we review content

We prioritise official NHS and GOV.UK guidance, then relevant professional-body information where needed.

Source links are checked on the review date shown above. Your midwife, GP, maternity team, fertility clinic, or employer can give advice that is more specific to your circumstances.

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Week 22

Track Your Due Date

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NHS Resources

Find trusted information on financial support, antenatal classes, and local maternity services.

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All Weeks

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