Second trimester
21 weeks pregnant
Your baby is about the size of a carrot
- First trimester1st trimester weeks 1–12
- Second trimester2nd trimester weeks 13–26
- Third trimester3rd trimester weeks 27–40+
By Clever Mum Parenting · Parenting guides
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How big is the baby at 21 weeks pregnant?
At 21 weeks pregnant, your baby is about the size of a carrot, roughly 26.7cm and around 360g. The baby's movements are getting stronger and more coordinated — you may notice patterns to when they're active. Their digestive system is practising for milk. These are typical averages — your midwife's measurements are the ones that matter for your pregnancy.
What might you feel at 21 weeks?
Most people at 21 weeks notice some mix of the symptoms below — and plenty notice none of them. Appetite is often strong now. Some experience swollen feet, indigestion or shortness of breath as the uterus rises. Stretch marks may appear on the bump, hips or breasts. None of this is a diagnosis; contact your midwife if something worries you.
Common symptoms this week
- Stronger, patterned movements
- Swollen feet by evening
- Indigestion beginning
- Possible stretch marks
Symptom lists are typical, never exhaustive — and having none of them is normal too.
What should you do at 21 weeks pregnant?
The useful job this week is practical, not medical. Start noting your baby's movement patterns. From now, getting to know what's normal for your baby matters — report any reduction to your maternity unit straight away. Pair it with the NHS week-by-week guide if you want a second description of the same stage.
Week 21 checklist
- Start tuning into your baby's movement pattern — from now, knowing what's normal for your baby matters
- Save your maternity unit's triage number in your phone
What antenatal care is due around 21 weeks?
These appointments, vaccines and deadlines fall around this stage. Your maternity team will confirm your own dates.
- Whooping cough vaccine (from 16 weeks). Offered in every pregnancy from 16 weeks, usually around 20 weeks. Antibodies pass to your baby before they can have their own vaccines at 8 weeks. Pregnancy and baby vaccines
- 20-week scan (usually 18 to 21 weeks). The mid-pregnancy scan screens for 11 physical conditions and takes around 30 minutes. It cannot find every condition, and it is your choice whether to have it. What the 20-week scan checks
- Tell your employer at least 15 weeks before your due date. GOV.UK says to tell your employer when the baby is due and when you want your leave to start at least 15 weeks before your due date — around 25 weeks pregnant. For Statutory Maternity Pay you also need proof of pregnancy, usually the MATB1 your midwife or GP can give you from 20 weeks before the due date. Estimate your 2026/27 maternity pay
What else is useful at 21 weeks?
Use the week page for size and symptoms; use the guides below for the decisions that actually sit in this window — pay, packing, car seats, labour signs.
21 weeks pregnant: common questions
How many kicks should I feel a day?
There's no set number — the NHS moved away from kick counts. What matters is your baby's own pattern: once you know their normal, any slowdown or change is the signal. Report reduced movements to your maternity unit immediately, day or night, and never wait until morning.
How big is my baby at 21 weeks pregnant?
At 21 weeks, your baby is approximately the size of a carrot, about 26.7cm and around 360g. These are approximate averages — every baby grows at its own pace.
What's happening at 21 weeks pregnant?
The baby's movements are getting stronger and more coordinated — you may notice patterns to when they're active. Their digestive system is practising for milk. For you: appetite is often strong now. some experience swollen feet, indigestion or shortness of breath as the uterus rises. stretch marks may appear on the bump, hips or breasts.
What appointments or vaccines are due at 21 weeks pregnant?
Around 21 weeks: whooping cough vaccine; 20-week scan; tell your employer at least 15 weeks before your due date. Your maternity team will confirm the dates that apply to you.
Which trimester is 21 weeks?
21 weeks pregnant is in the second trimester. The first trimester runs to the end of week 12, the second from weeks 13 to 26, and the third from week 27 to birth.
Sources & further reading
This is general information, not medical advice — every pregnancy is different. For anything that worries you, and for all your antenatal care, speak to your midwife or GP. If your baby's movements ever slow down or change, contact your maternity unit immediately, day or night.