Q&A: I'm 19 weeks and feel "vibrations." What could this be?

What you're referring to is something that used to be called "quickening."

Quickening is an old term that specifically refers to the expectant mother's first perception of life within her womb—actually, first perceived fetal movement within her uterus. It will feel at first like little butterflies below your navel. It is first felt at about 18-20 weeks in a woman having her first baby, and the flutterings will organize over the next few weeks into discrete jumps and then kicks.

Medically, quickening is no big deal in these days of ultrasonigraphic videos of baby in the first trimester, but it should still be a personal thrill—your baby is knocking on your door and saying, "I'm here! I exist! Love me!"