Your Pregnancy: 4 Weeks

How your baby's growing:

This week marks the beginning of the embryonic period. From now until ten weeks, all of your baby's organs will begin to develop and function. As a result, this is the time when she'll be the most vulnerable to anything that might interfere with her development.Right now your baby is an embryo consisting of two layers: the epiblast and the hypoblast, from which all her organs and body parts will develop. The primitive placenta is also made up of two layers at this point. Its cells are tunneling into the lining of your uterus, creating spaces for your blood to flow into so that the developed placenta can provide nutrients and oxygen to your growing baby when it starts to function at the end of this week. Also present now are the amniotic sac that will house your baby, the amniotic fluid that will cushion her as she grows, and he yolk sac that produces your baby's red blood cells and helps deliver nutrients to her until the placenta is ready to take over this duty.

How your life's changing:

This week, you should be able to find out if you're pregnant. How will you know for sure? Take a home pregnancy test; they're no different from the tests used in most practitioner's offices.
If the test is positive, call your practitioner's office and schedule your first prenatal appointment. Many practitioners won't see you until you're at least 8 weeks along, but if you're taking any medications — prescription or over-the-counter — ask now whether it's safe to keep taking them, and alert your doctor to any other issues of concern. You should already be taking a prenatal vitamin, but be sure to start now if you aren't. The next five weeks are critical to your baby's development. The rudimentary versions of the placenta and umbilical cord, which deliver nourishment and oxygen to your baby, are already functioning. Your baby is now exposed, via the placenta, to what you take into your body, so make sure it's healthy.