Fetal Development Weeks 36 Through 40

Week 39

Only five percent of babies decide to greet the world on their due date, so yours could arrive at anytime now. While you're waiting, mull over this word of the week: fontanels. These are the two soft spots on a baby's head where the skull bones don't yet join together. The fontanel allows the flexible skull bones to shift and bend as baby journeys through the birth canal, making for an easier trip without damaging the brain. Don't panic if your little one's head looks elongated or even cone-shaped right after birth -- the bones will quickly remold themselves into a rounded shape. During the course of baby's first year, the skull will harden, and by 18 months, the fontanels will have disappeared.

At the time of birth, the baby has a total of 300 bones. Some of these bones will fuse together as the baby grows; adults have a total of 206 bones.

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