Your baby measures about 6.5 inches/ 16.5 centimetres from crown to rump and is steadily gaining weight. A whitish coat of a slick, fatty substance called vernix caseosa begins to cover your baby and protects the skin during its long immersion in amniotic fluid. It also eases delivery. The baby's swallowing more this week, good practice for the digestive system. After your baby takes in amniotic fluid, his body absorbs the water in the liquid and moves the rest into the large bowel.

http://www.babycenter.ca/pregnancy/fetaldevelopment/20weeks/