Week 21 of pregnancy
By 21 weeks, your baby weighs around 350g. They now weigh more than the placenta. The placenta will keep growing throughout pregnancy, but not as fast as your baby.
They are now covered with very fine, soft hair. The hair is called lanugo. The purpose of this hair is not known, but it may keep the baby at the right temperature. The lanugo usually disappears before birth.
Week 22 to 23 of pregnancy
Your baby is getting into a pattern of sleeping and waking. This may not be the same pattern as yours. When you're in bed at night and trying to sleep, they may be wide awake and moving about.
Their lungs are not yet working properly. Despite this, your baby is practicing breathing movements. They are preparing for life outside the uterus (womb). They get all their oxygen from you through the placenta (afterbirth) until they are born.
Week 24 of pregnancy
Your baby has a chance of survival if they are born now and given lots of support. But most babies born before this time cannot live. This is because their lungs and other vital organs are not developed enough.
The care now available in baby (neonatal) units means more and more babies born early do survive. There are greater risks of disability for babies born around this time. But there are treatments available. These may help reduce the chance of problems for your baby.