Four weeks into your pregnancy, your baby is now an embryo consisting of three different layers. The inner layer, known as the endoderm, will develop into your baby's lungs, liver, and digestive system. The middle layer, called the mesoderm, will eventually be your baby's bones, muscles, kidneys, sex organs, and heart. Finally, the ectoderm, or outer layer, will make up your baby's tissues and organs such as the skin, hair, eyes, and nervous system. A maternal blood or urine test this week would show a positive result because the embryo is secreting human Chorionic Gonadotropin (hCG), the pregnancy hormone. Home pregnancy tests, which test for hCG in the urine, may show a positive result but are not as accurate as blood tests this early in pregnancy

Until now, the embryo has been a mass of cells, but by this point in your pregnancy a distinct shape begins to form. The neural tube, which will eventually form into the spinal cord and brain and is also called the primitive streak, runs from the top to the bottom of the embryo. The top part of the neural tube has begun to flatten out and will eventually form the front part of the brain. A bulge in the center of the embryo will develop into your baby's heart. The use of a home pregnancy tests could be positive this week. If you want to use a home pregnancy test, testing in the morning will give the most accurate results - the first urine of the day will contain the highest levels of the pregnancy hormone, hCG.

Even if you have not felt the onset of nausea yet, you'll want to eliminate certain foods from your diet when you're pregnant. Foodborne illnesses, such as listeriosis and toxoplasmosis, can be life-threatening to an embryo and may cause birth defects or miscarriage. Here's a list of foods you'll want to avoid: soft cheeses such as feta, goat, brie, Camembert, and blue cheese unpasteurized milk and juices raw or undercooked meats, including hot dogs and deli meats raw eggs or foods containing raw eggs, including mousse and tiramisu raw shellfish pate Toxoplasmosis can also be spread from soiled cat litter boxes, so if possible have someone else clean the litter box during your pregnancy.

The journey continues into the 7-8 weeks, and you can follow the journey here

About the Author
Chandra is a freelance contributing writer to http://www.pregnancy-resource-guide.com and http://www.joyofpregnancy.com online guides to pregnancy and birthing. She is also a frequent contributor to websites on parenting and raising your children. More articles can be viewed at the links above...