Week 12 Update:

Your Baby in Week 12 of Pregnancy:
By now, your baby weighs a full half-ounce and is about the size of a large plum. Most of his systems are in place, though there's still plenty of maturing to do. For one thing, his fetal digestive system is beginning to practice contraction movements necessary for eating, and his bone marrow is busy making white blood cells — weapons against germs once he's out of your safe haven. The pituitary gland (at the base of the brain) has started producing the hormones that'll enable him (or her) to make babies of his (or her) own in a couple of decades or so.
Learn more about your baby in week 12 and fetal organs and systems.

Your Body in Week 12 of Pregnancy:
If all those changes in your baby sound dizzying, that may just be you dealing with yet another problematic pregnancy symptom: Lots of women experience occasional dizziness and/or feel faint due to progesterone, which causes increased blood flow to your baby by relaxing your own blood vessels. The decrease in blood flow to your body and brain, along with typically lower blood-sugar levels during pregnancy, can set your world a-spinning. Do your part to keep your equilibrium by eating regularly, getting adequate rest, and standing up slowly.
Learn more about your body in week 12 and dizzy spells during pregnancy.