Week 21 of Pregnancy

Written by Amina Hatia RM and medically reviewed by Marley Hall RM

Published on February 7, 2022
Live & Online 60,000+ Community

After all of the excitement of last week with your 20 week scan, you’re probably feeling more and more pregnant and now beginning to enjoy this next stage of your pregnancy.

There are lots of changes ahead as preparation begins for the third trimester and life with a baby – so don’t be surprised if it feels like a busy period from now on.

Your midwife will have discussed with you, at your booking appointment, the vaccinations that are offered in pregnancy – with the whooping cough vaccine being offered in the second trimester. It’s quite common for the discussion or reminder to come up again after you’ve had your 20 week scan.

Whooping cough is an infection that can severely affect the respiratory system. The symptoms are very severe coughing fits, which can be serious in very young babies. New-born babies are at risk of infection until they receive their first vaccinations at 8 weeks, which is why you are advised to have the vaccine to boost your antibodies which are then passed via the placenta onto your baby.

In the UK, the vaccine you will be offered is the Boostrix IPV – which also offers protection against polio, diphtheria and tetanus and research indicates it is very safe in pregnancy for both mum and baby.

How big is my baby?

At 21 weeks your baby is the size of a large carrot, weighing a scrumptious 350 grams and measuring from top to tail end about 26 centimetres.

What happens in week 21 of pregnancy?

At 21 weeks your baby’s digestive system starts to mature and develop ready for their birth. It will take time to develop and the majority of nutrients your baby is getting is still via the placenta. 

The changes in the digestive system that you can’t see happening include; the pancreas beginning to make enzymes – which are needed for digestion – and baby’s small intestine growing and starting to absorb nutrients from amniotic fluid that your baby has started to swallow.

Pregnancy symptoms in week 21

As your bump starts to grow rapidly over the next few months, one of the changes that many expect or worry about is stretch marks.

Stretch marks are synonymous with pregnancy – but it may surprise you to know that not everyone gets them or that they appear differently of different skins. They can appear as pink, red, brown, silvery or sometimes purplish streaks and are caused by tiny little tears in the layers of tissue under your skin as it stretches due to your changing shape.

Despite the many myths and products on offer promising to help you avoid getting stretch marks, in reality whether you get them or not depends on your skin. However, keeping yourself well hydrated, moisturising, eating well and exercising regularly will also help.

Week 21 pregnancy tips

  • Have you thought about how you plan to feed your baby? – Breastfeeding is the best and healthiest option for your new born baby, but it’s important to understand and learn about breastfeeding in the antenatal periods as well as other options. Our antenatal courses – both 4 week and weekend courses, cover preparing for breastfeeding in detail and lots of helpful advice from our practising midwives.

  • If you haven’t already, discuss the whooping cough vaccine with your midwife and find out when and where to get it. Often, it’s available in your maternity unit, but your GP can arrange this for you too.

  • How’s the baby shopping plans going? – There are so many choices available, and it can all feel overwhelming.  Check with friends and family who have recently had a baby about what they found really helpful, what wasn’t so much and what turned out to be a waste of money!

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