No more doubt!

So it is done! The fastest, boldest, and most ambitious sperm reached your egg and fertilized it. The egg turns into a zygote and begins to divide rapidly: 2 cells, 4, 8, 16. At the same time, it moves towards its future home — the womb. The zygote's journey through the fallopian tubes takes about 6 days.

During this time, your microscopic miracle is growing up: it already consists of hundreds of cells and is called a blastocyst (don't worry, you'll soon come up with a nicer nickname). By the end of the 3rd week, the blastocyst reaches the uterine cavity, chooses a comfortable spot, and attaches to the endometrium — this is called implantation. From this point on, part of the cells will develop into the baby, and the other part into the placenta, which will be fully formed by week 12.

The part of the cells that grows into the placenta will begin producing the pregnancy hormone hCG (human chorionic gonadotropin), which tells your ovaries to stop ovulating and triggers an increase in estrogen and progesterone production. These hormones keep the uterus from shedding the upper layer of the endometrium (as happens in menstruation), protecting the tiny passenger, and stimulate the growth of the placenta.

The baby resembles a bubble: a cavity forms inside the blastocyst, where amniotic fluid begins to accumulate. This fluid will protect your baby until birth. Right now, your tiny blastocyst begins to receive oxygen and nutrients (and get rid of waste) through a primitive circulation system made up of microscopic tunnels connecting the embryo to blood vessels in the uterine wall. The baby will get the hang of this by the end of next week.

Measuring baby:
Height 0.0079 in. (0.2 mm)