Week 4

Your Baby's Development
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.

Your Body
The hormones your baby is secreting may cause you to experience the first symptoms of pregnancy this week. Symptoms such as fatigue, tingling or aching breasts, or nausea might lead you to believe your period will be starting any day because the first pregnancy symptoms resemble premenstrual syndrome. You won't know until later that it's your baby causing the symptoms!