In the third week of your pregnancy, you conceived. This week, the egg that was fertilized in the last week of your pregnancy has moved into your uterus where it will live for the next nine months. Once the embryo sets up its new home in your uterus, it divides in half: half of the cells form your baby, and the other half form the placenta.

Your Baby at Week 4 of Pregnancy

In week four, your baby is tiny—only a millimeter in diameter. However, the changes that your newly conceived baby are going through right now will become the basis for its organ development for the next ten weeks. Healthy organ development is critical for a growing fetus, so it’s important that from this point on you avoid ingesting or exposing yourself to potentially unsafe chemicals in your environment.

Keep in mind that the things you eat and drink, any medicine you take, and any products you inhale (think spray tan or hairspray particles in the air) or apply to your skin may impact your baby’s development. The fourth week of your pregnancy is the perfect time to start doing research on which medicines and skincare products are safe during pregnancy and which should be avoided.

Your obstetrician can be a valuable resource in this research as well, so don’t be afraid to go in for your pregnancy confirmation test with a list of questions.

Your Body at Week 4 of Pregnancy

At this point in your normal cycle, your body would be preparing to shed its uterine lining and begin menstruation within the next week. However, since you’re pregnant, your body will not go through this process, and you will not have another period until after your baby is born.

It’s possible in your fourth week of pregnancy to still get a false negative on a home pregnancy test. If you get a negative result this week but don’t start your period in the next week, take another test. Home pregnancy tests can generally give you a more accurate result in the fifth week of your pregnancy. Once you’ve confirmed that you’re pregnant, set up an appointment with your obstetrician.

While you’re probably not noticing many changes with your body this early during your pregnancy, this is an important time to start taking care of yourself to make sure your body is prepared. If you haven’t already, start taking a prenatal vitamin daily after getting a positive pregnancy test in order to make sure you’re getting all of the nutrients you need to support your developing child.

Preventing Stretch Marks

Over the next few weeks, your body will start to show signs of pregnancy. The signs will be minimal at first—other people may not even notice you’re getting a little rounder—but the beginnings of your pregnancy growth signal an important time to start using a stretch mark prevention product. During your pregnancy, you’ll be at high risk for developing stretch marks, and using a stretch mark prevention lotion or cream may strengthen your skin and help prevent stretch marks.