Until 10 weeks, every brain is female. Then, in boys, a huge surge of testosterone hits the brain, killing cells in the communication center and growing them in the sex and aggression center. It also helps some coordination neurons develop better than they do in females. In either sex, baby's chin, eyelids, and arms can now sense touch.
Right around this week (generally between 10-12 weeks), you may choose to have the chorionic villus sampling test (also called CVS). A small sample of cells is removed from the developing placenta. Since the placenta is made up of cells that derive from the same fertilized egg as the fetus, it's an ideal resource for DNA that can reveal genetic abnormalities in the baby.
Baby's length (CTR): 1.61 in
Baby's weight: 0.25 oz