Although your baby's skeleton is hardening, the skull is quite pliable. It needs to be, so that during birth the plates of the skull can move and overlap to allow the baby to fit through the birth canal. Even after birth, the skull bones won't fuse for many years. This allows the skull to accommodate the child's growing brain.
By now, you may have felt a few Braxton Hicks contractions. Braxton Hicks contractions are a tightening of the uterine muscles. They can last 30 seconds to a few minutes. They can feel strange, but they're not usually painful. They go away. It's thought that these contractions are like uterine warm-ups, helping to tone and ready your body for the intense contractions of true labor.
If you're having Braxton Hicks contractions, use them as a chance to practice for real labor. Try breathing and visualization techniques to relax through each surge. Call your healthcare provider's office only if the contractions don't go away, if they're frequent (you have more than 4 in an hour), or if they come with vaginal discharge of any kind.