21 weeks pregnant
Second trimester about 4 months
At 21 weeks pregnant, your baby is about the size of a carrot.
Baby this week
About 26cm. The baby is swallowing amniotic fluid and practicing digestion. Eyebrows and eyelashes are forming, and the baby is developing sleep and wake cycles.
Did you know? By week 21, the baby has developed distinct sleep and wake cycles — you may notice it's more active at certain times of day, often when you're lying still at night.
What she may be feeling
- Regular strong fetal movement
- Back pain
- Heartburn
- Braxton Hicks
- Swelling
- Stretch marks
- Leg cramps
- Fatigue returning slightly
Tips for her this week
- Baby movements should now be regular and recognizable — you may notice patterns.
- Braxton Hicks can increase — stay hydrated, as dehydration can trigger them.
- Heartburn may worsen — small meals, antacids safe for pregnancy, and staying upright help.
- Start thinking about your maternity leave start date.
For partners
- Talk to her belly regularly — your voice is one of the most recognizable sounds to the baby.
- The kicks may be strong enough now that you can feel them clearly from the outside.
- Start building the baby registry if you haven't already — people will start asking.
- Research your hospital or birthing center's protocols: parking, check-in, support person rules.
Partner to-do list
- Feel kicks regularly and respond to them
- Build or finalize the baby registry
- Research your birthing location's policies
- Start an infant sleep research project — sleep is what you'll need to understand
This week together
- Finalize the baby registry
- Tour the birthing facility if you haven't
- Discuss maternity leave start date
- Research infant sleep strategies
When to call your doctor or midwife
Contact your care provider right away, or call emergency services, if she has:
- Heavy bleeding
- Regular painful contractions
- Fever
- Signs of preeclampsia: severe headache, vision changes, sudden swelling
Trusted guidance: NHS: Pregnancy · NHS: Pregnancy complications · ACOG: Pregnancy · Pregnancy Info: Your pregnancy
Common questions
How big is the baby at 21 weeks?
At 21 weeks pregnant, your baby is about the size of a carrot. About 26cm.
How many months is 21 weeks pregnant?
21 weeks pregnant is about 4 months, in the second trimester.
What can partners do at 21 weeks?
Talk to her belly regularly — your voice is one of the most recognizable sounds to the baby. The kicks may be strong enough now that you can feel them clearly from the outside.