While some may think that as soon as a baby is conceived, it looks like a baby; this actually isn't the case at all. For the first three weeks of pregnancy the baby is only an embryo with no defining human characteristics. Come week three, however, and things begin to change; while the fetus still may not look quite like what a baby looks like, it begins to develop the characteristics that will make it baby.

Beginning in week three of pregnancy the embryo becomes a fetus; while it is only 1/5 of an inch long at this point, a heartbeat develops. Of course the mother cannot hear it, but with the help of modern medicine, the doctor can.

At this time, the arms and legs begin to develop; nubs begin to protrude where the arms and legs will grow to full length. It is also towards the end of week three of the pregnancy that the fetus begins to develop a digestive system. Until now he has completely relied on his mother for food, but the digestive system takes a lot of time to fully develop which is why it begins so early in pregnancy.

Because week three becomes such a defining time when embryo becomes fetus, it's imperative that the mother begin to eat healthfully and with baby in mind. She should go to see the doctor as soon as she discovers she is pregnant and get on prenatal vitamins and talk about a pregnancy diet. Even if a woman isn't quite pregnant yet but hopes to be soon, she should begin to get enough folic acid, protein, calcium and iron; these are all vital to the new and developing fetus.

Folic acid especially helps to prevent abnormalities of the brain and spinal cord. Calcium is essential for the development of the bones, and protein for development of the tissues. While a woman may not have had a healthy diet previous to conception, now she is living for two and she must become hyper aware of what she puts into her body that nourishes both her and the unborn child.

Many things can affect the fetus developmentally in these first few weeks of pregnancy so it's imperative that at the first sign of pregnancy a woman see her doctor to begin a healthy regimen; after all, a healthy diet contributes to a healthy baby.