Week 3!

What's going on in my womb now? A lot. Our baby-in-the-making is just a tiny ball consisting of several hundred cells that are multiplying madly. Once the ball of cells (called a blastocyst) takes up residence in my uterus, the part of it that will develop into the placenta starts producing the pregnancy hormone hCG (human chorionic gonadotropin), which tells your ovaries to stop releasing eggs and triggers increased production of estrogen and progesterone (which keep your uterus from shedding its lining — and its tiny passenger — and stimulates placental growth).

Meanwhile, amniotic fluid is beginning to collect around the ball of cells in the cavity that will become the amniotic sac. This fluid will cushion our baby in the weeks and months ahead. Right now, our little blastocyst is receiving oxygen and nutrients (and discarding waste products) through a primitive circulation system made up of microscopic tunnels that connect our developing baby to the blood vessels in my uterine wall. The placenta won't be developed enough to take over this task until the end of next week.