You've reached the end of the third trimester, and what an incredible period of development it's been! Your baby has been growing like a weed: he may have tripled in length since he was 12 weeks old. His bony skeleton is fully assembled but not yet connected at the joints. The bones are able to support the fetus structurally, though, allowing him to twist and move around in the uterus.

Muscle coordination is now such that your baby can suck his thumb. Don't worry, that's a good thing: sucking his thumb calms the little one and strengthens his jaw and cheek muscles in preparation for feeding. The lungs, liver, and immune system are continuing to develop.