21 weeks pregnant
Your baby now outweighs the placenta.
In short
At 21 weeks your baby is about the size of a carrot, around 27.4 cm long and 398 g. Your baby now outweighs the placenta.
- Second trimester, week 21 of about 40.
- Start noticing when your baby tends to be active. If movements ever slow down, change or stop, contact your maternity unit straight away.
Turn your baby round in 3D every week in the free Lullagram pregnancy section
Your baby now weighs more than the placenta, which keeps growing too but more slowly. Fine, soft hair called lanugo covers the body and may help keep your baby at the right temperature.
How big is my baby at 21 weeks?
At 21 weeks your baby is about the size of a carrot, around 27.4 cm long and 398 g. Before about 14 weeks babies are measured from crown to rump; after that the figure is head to heel. These are typical figures from fetal growth charts. Your own baby may be bigger or smaller, and your scans are what count.
What is my baby doing at 21 weeks?
- Your baby now weighs more than the placenta, which keeps growing too but more slowly.
- Fine, soft hair called lanugo covers the body and may help keep your baby at the right temperature.
- Your baby can hear noises and voices from outside the womb.
- Hair and eyebrows are developing.
What changes for me at 21 weeks pregnant?
- Your centre of gravity is changing and your joints are looser, so you may feel a little unsteady.
- Your baby may be wide awake and moving just as you're trying to settle down for the night.
- Naps during the day can help make up for broken sleep.
What is a good tip for this week?
Start noticing when your baby tends to be active. If movements ever slow down, change or stop, contact your maternity unit straight away.
What can a partner do this week?
Take over some evening jobs so they can put their feet up.
What should I know in Ireland at 21 weeks?
Nothing Ireland-specific falls in this week. Your care continues under the Maternity and Infant Care Scheme with your GP and maternity unit. See the full Irish pregnancy timeline for what is coming up.
When to get help: If you have a fall or a knock to your tummy, contact your midwife, GP or maternity unit, especially if you are rhesus negative, as you may need an anti-D injection. HSE: when to get help.
Want these updates on your phone? The Lullagram app has a free pregnancy section with this week-by-week guide, Irish dates worked out from your due date, a contraction timer and more. When your baby arrives, the baby tracker is ready in the same app.
Guides for your pregnancy: pregnancy care in Ireland · maternity leave and benefit · hospital bag checklist · popular baby names · free IVF in Ireland · due date calculator
Sources and guidance
This page is written to be consistent with the official guidance below. It is general information for parents in Ireland, not medical advice. Links checked 23 September 2026.
I've used the app since my now 3 month old was born and it's honestly brilliant. Very handy when me and my husband were doing handovers, no one needed to be woken up or questioned! Great resource for the public health nurse when we had concerns about feeding etc, it was all recorded in the app. It's also really refreshing to have an app like this geared towards parents in Ireland.