Your baby is growing by leaps and bounds, and his sixteenth week of fetal growth is no exception. You may have felt a few flutters in your tummy around this time. This is referred to as quickening, and you are feeling your baby's first movements. He is getting stronger and exercising his extremities frequently. Your babies nails are growing rapidly at this time, and so are her arms and legs. His bones and muscles are strengthening, too.