What Causes A Dent In The Skull During Pregnancy?

hi doc, i have a skull dent for over 15 yrs now.i never had this before.it appeared only when i was pregnant with my 1st born way back 1995.i went to the 3 neuro's already. only 1 explained a bit ok.he said it's somewhat a metopic suture.is this normal? i have occasional headaces on the left side ever since.