16 weeks, 4 days

Boo is now about the size of an avocado (about 11.6 cm long from crown to rump and weighing approximately 100 grams). In the next three weeks he/she will go through an tremendous growth spurt, doubling weight and adding inches to length.

In or out of the womb, babies are playful creatures. Boo has probably already discovered their first toy -- the umbilical cord -- which he/she will enjoy pulling and grabbing. Sometimes it may even be clutched so tight that less oxygen gets through, but don't worry -- it won't be held onto long enough to harm him/herself.

The circulatory system and urinary tract are in full working order, and Boo's inhaling and exhaling amniotic fluid through his/her lungs.