The body changes in surprising and complex ways during pregnancy. During the first week of pregnancy, most of the changes that occur within the body depend on whether a woman counts from her last menstrual period or from conception. If a woman counts from the first day of her last menstrual period, her body usually sheds her uterine lining in the form of a menstrual period during this week. However, if a woman counts the first week from conception, the cells that will develop into a baby are usually undergoing rapid changes within her reproductive system.
Figuring out what happens to the body during the first week of pregnancy can be complicated by the fact that doctors count weeks of pregnancy from the first day of a woman's last menstrual period. However, this is before a child is conceived, which means that a woman is not actually pregnant. If a woman uses this 40-week method to consider the body changes of pregnancy, the body is shedding its uterine lining at this stage. A woman usually has menstrual bleeding at this time, and some women may experience pelvic cramping, mood swings, and an increase in acne as well. About 14 days after the start of this week, a woman's ovary will usually release an egg that can be fertilized by her partner's sperm.
If a woman considers the first week after conception rather than the first week of pregnancy as recognized in the medical world, she will learn that a complex series of activities are occurring within the body at this time. Once a sperm cell fertilizes an egg cell, a complicated process of cell multiplication and growth begins. This multiplication and growth involves the cells that will eventually become the embryo and placenta. The group of cells does not look like a baby nor does it look like a human being at this point in development.
In most cases, a woman will not notice any changes in her body during this first week of pregnancy. At this point, a woman usually hasn't missed a period yet. Some women say they notice symptoms as early as the first week after conception. However, they may notice what seem like symptoms only because they are hoping to get pregnant or because they are concerned about the possibility of an unplanned pregnancy. If a woman experiences real symptoms during this time, such as nausea, fatigue, or breast tenderness, they may be caused by hormonal changes in the body.