What's happening with your baby at 21 weeks
At 21 weeks, your baby is about the length of a carrot — roughly 26.7 cm from head to heel — and weighs around 360 grams. Movements are becoming stronger and more coordinated as muscles and the nervous system mature.
Your baby is swallowing more amniotic fluid now, which helps the digestive system practice its future job. This also supports lung development, since the fluid moves in and out of developing airways.
Eyebrows and eyelids are fully formed, and taste buds are developing. If you're carrying a girl, her uterus and vagina are already formed; if you're carrying a boy, the testes haven't yet descended — that typically happens later.
Common symptoms at 21 weeks
Your bump is noticeably rounder, and you may see skin changes like a dark line down your belly (linea nigra) or darker patches on your face (melasma). These are common and usually fade after delivery.
Increased vaginal discharge, mild swelling in your feet and ankles, backaches, and leg cramps — especially at night — are all typical around this stage. Round ligament pain may still come and go as your uterus keeps growing.
Some people notice increased appetite and steadier energy in the second trimester, though heartburn and constipation can persist. Every pregnancy feels a bit different, so your experience may not match someone else's week by week.
Are Braxton Hicks contractions normal at 21 weeks?
Yes — some people start noticing Braxton Hicks contractions around 21 weeks, though many won't feel them until later. These are brief, irregular tightenings of the uterus, often described as a painless squeezing rather than a cramp.
Braxton Hicks tend to ease with rest, position changes, or drinking water, and they don't get progressively closer together. If contractions become regular, painful, or increase in frequency before 37 weeks, that's different from Braxton Hicks and warrants a call to your provider.
Not everyone notices Braxton Hicks at all in the second trimester, and that's normal too. They're a sign your uterus is limbering up, not a sign anything is wrong.
What to do this week
Start paying attention to your baby's movement patterns, even though you're not yet tracking formal kick counts — that usually starts in the third trimester. Getting familiar with your baby's typical activity now makes changes easier to notice later.
Ask your provider when your glucose screening test for gestational diabetes will be scheduled; it's usually done between 24 and 28 weeks. If you have risk factors, your provider may test earlier.
Keep up with prenatal vitamins, particularly iron, since your blood volume is expanding quickly during this stage. Gentle exercise, like walking or prenatal yoga, can help with backaches and energy levels.
When to call your provider
Call your provider the same day for vaginal bleeding, fluid leaking, contractions that come regularly before 37 weeks, or a sustained severe headache — especially with vision changes or swelling in your face or hands.
If Braxton Hicks contractions become painful, frequent, or don't ease with rest and fluids, mention this to your provider rather than waiting it out. It's always reasonable to call with a concern rather than guess.