From TheBump.com: Your adorable little fetuses (or is it fetii?) are busy with thumb sucking, toe wiggling, and (not so cute but equally amazing) making urine and breathing amniotic fluid as the liver, kidneys and spleen continue to develop. Lanugo (thin, downy hair) is growing all over their bodies for warmth.
"Thin downy hair?" Sounds like Mark's current attempt at a pregnancy beard. I'll try to post a picture of Mark's "lanugo" soon.