21 weeks

Fetal development in pregnancy week 21:

Your beautiful little miracle-gro baby will be putting on a full ounce and a half this week (and weighing up to 16.5 ounces), but that’s just the beginning! Within the next five weeks, they’ll really be packin’ it on! For now, we’re pleased to report the addition of rapid eye movement (REM) a key component to any healthy baby’s sleep schedule. While in the dermatology department: their thin soft skin is very red, rather translucent, and a bit wrinkled. Not to worry, it’s not a premature aging disease. It's just their clever little body setting them up with extra space that will smooth out once your little one starts packing on the baby-fat. That won’t be for a few more weeks, though. So for the time being, your munchkin is still a little lean mean growing machine! The beginnings of what is commonly called “brown fat” is just starting to fill in to help your baby retain some body heat, which is crucial as they’re not yet capable of regulating their own body temperature.