Week 21 of Pregnancy | How Big is Your Baby at 21 Weeks?

Pregnancy is a time of huge change for you, your body and your life. Our guide will help you through this amazing time, letting you know what to expect at each stage and, most excitingly, what your baby is up to each week.

Your baby is now the size of a large banana!

At 21 weeks of pregnancy, your baby is the size of a large banana (last week it was an average banana!) from crown to heel and they weigh around 400g (14oz).

It’s during the 21st week of pregnancy that your baby starts to weigh more than their placenta (1). The placenta does carry on growing, but at a slower pace than the baby it’s supporting.

By now your baby’s tongue is fully developed and they’re practising reaching for and grasping their umbilical cord.

They’re also covered in very soft, downy hair, called lanugo (2), this week.

Baby’s digestive system is starting up!

While the placenta is still giving your baby most of their nutrition, their digestive system is getting itself into gear so it can take this role after birth.

Their pancreas is starting to produce some of the enzymes (3) which will break down food and your baby’s small intestine is lengthening and starting to absorb nutrients from your amniotic fluid.

Your baby’s already recognising your voice!

If you sing or talk to your baby, he or she will be able to recognise you now (4), so start a daily routine of reading a story or singing a song - it's a very special time when your baby is learning to recognise your voice (and doesn't get embarrassed by your singing...) so enjoy it.

Your 20-week scan

 You probably had your anomaly scan (5) last week, but there’s a chance it could be this week, so find out more about it here.

How you’re feeling at 21 weeks pregnant

As your bump gets bigger, your centre of gravity changes (6) and so you might feel a bit wobbly or unsteady on your feet now and again. The pregnancy hormone relaxin softens your joints (7) a bit, which can also make you a little clumsy. If you fall over, try not to worry as your baby is very well protected in your womb, but do tell your midwife so they can check you over if necessary.

If you travel on public transport a lot, think about getting a “Baby on Board” badge so other commuters are more likely to offer you a seat or any other help.

You’re definitely looking pregnant by now, so you might start to get attention from fellow commuters, shoppers and, well, total strangers. You might enjoy having a quick chat and listening to advice, but sometimes it can feel a bit much so in these instances, a polite “Thanks, I’ll think about it,” usually does the trick.

Staying healthy at 21 weeks pregnant

You’ve already established some healthy pregnancy eating habits (8) and now is the time to think about your baby’s bones. They’ll need calcium and vitamin D to help them to build strong bones and teeth.

Eat lots of green leafy vegetables for the calcium (as well as the fibre) and either take a vitamin D supplement or try to spend more time out in the sunshine. Even if you're already eating a balanced diet, your midwife might suggest a vitamin D supplement (9), especially if you cover up when you're outside or if you have darker skin.

What you need to think about at 21 weeks of pregnancy

You’re into the second half of your pregnancy now and if you’ve found out whether you’re having a boy or a girl you can start to think about names a bit more seriously.

If you’re feeling your baby’s movements (10) by now, then you might want to start monitoring and counting them. You’ll notice a pattern, with your baby being more active at some times of the day (and night) than others.

Citations and References

(1) National Health Service (NHS). ‘Pregnancy Week by Week. You and Your Baby at 21 Weeks Pregnant.’ 2021. Web. www.nhs.uk/pregnancy/week-by-week/13-to-27/21-weeks placenta weight

(2) National Health Service (NHS). ‘Pregnancy Week by Week. You and Your Baby at 21 Weeks Pregnant.’ 2021. Web. www.nhs.uk/pregnancy/week-by-week/13-to-27/21-weeks (lanugo)

(3) National Institutes of Health (NIH). ‘Development of the Human Pancreas and its Exocrine Function.’ 2022. Web. www.ncbi.nlm.nih.gov/pmc/articles/PMC9557127

(4) National Health Service (NHS). ‘Relationships and Wellbeing in Pregnancy. Attachment and Bonding During Pregnancy.’ 2023. Web. www.nhsinform.scot/ready-steady-baby/pregnancy/relationships-and-wellbeing-in-pregnancy/attachment-and-bonding-during-pregnancy

(5) National Health Service (NHS). ‘Your Pregnancy Care. 20-week Screening Scan.’ 2021. Web. www.nhs.uk/pregnancy/your-pregnancy-care/20-week-scan

(6) Physiopedia. ‘The Biomechanics of Pregnancy.’ Web. www.physio-pedia.com/The_Biomechanics_of_Pregnancy

(7) Cleveland Clinic. ‘Body Systems and Organs. Relaxin.’ 2022. Web. my.clevelandclinic.org/health/body/24305-relaxin

(8) National Health Service (NHS). ‘Keeping Well in Pregnancy. Have a Healthy Diet in Pregnancy.’ 2023. Web. www.nhs.uk/pregnancy/keeping-well/have-a-healthy-diet

(9) National Health Service (NHS). ‘Keeping Well in Pregnancy. Vitamins, Supplements and Nutrition in Pregnancy.’ 2020. Web. www.nhs.uk/pregnancy/keeping-well/vitamins-supplements-and-nutrition

(10) National Health Service (NHS). ‘Keeping Well in Pregnancy. Your Baby’s Movements.’ 2021. Web. www.nhs.uk/pregnancy/keeping-well/your-babys-movements