The first trimester is just the beginning of your pregnancy. There are a million changes happening to your body as well as your baby. This is the time wherein you will learn about pregnancy tests, morning sickness and prenatal care as your start your pregnancy off with a healthy beginning.

Your actual pregnancy begins at the time when the egg is fertilized by a sperm cell. During the following week, the fertilized egg grows into a blastocyst (something like a microscopic ball of cells), which implants itself on the wall of your uterus. This implantation triggers a series of hormonal and physical changes in your body.

Once you enter the third weeks of growth, your baby will be in what is called the embryonic stage, during which the major body organs are developed. This is the most fragile time of your pregnancy, as the embryo is vulnerable to harmful substances, such as alcohol, smoking, and other infectious diseases.

Read on to learn more about what happens to you and your baby as each week passes.