Week 1-4

Weeks 1 and 2

If successful, fertilization occurs in the fallopian tube and by the end of the first week cell division and differentiation have occurred, and the blastocyst (the differentiated and specialized group of cells that are the foundation of the baby) has implanted itself in the mother's uterine lining. During these first two weeks you are not likely to know that you are pregnant yet as you have not missed a menstrual cycle. Conception is typically presumed to have occurred two weeks after the last menstrual cycle, thus, this point is used as the official beginning of pregnancy and as a reference for a primary calculation the due date.

Week 3

The baby: The zygote is very small at this point, perhaps the size of the head of a pin. It is comprised of approximately 100 cells which are growing and multiplying at a rapid rate. The outer layer of this group of cells will eventually become the placenta and the inner layer will further develop and become the embryo from which the fetus is formed.

The mother: There are no obvious physical changes in the mother's body as of yet. Most women still will not have missed a menstrual period and may have no idea that they are pregnant. Quality store bought home pregnancy tests will be able to give accurate and immediate results at this phase in pregnancy.

Signs of PregnancyOther Possible Causes of these Symptoms

Missed menstrual cycleChange in weight, fatigue, stress, anxiety, stopping birth control

Nausea without vomitingStomach disorder, food poisoning, stress

FatigueStress, depression, flu, anemia

Breast Changes and TendernessHormonal imbalance, birth control, menstruation

Frequent UrinationDiabetes, Urinary tract infection, diuretic consumption

Week 4

The baby: the baby is very small at this point, perhaps 0. 014 - 0. 04 inches in length and comprised of 150 cells. The embryo is more deeply implanted in the uterine lining and the amniotic cavity and placenta are beginning to form. The layers of cells of the embryo are specialized by function. The inner layer will become the respiratory and digestive organs, the middle layer will develop to form the skeletal system, the sex organs, the kidneys, circulatory system and muscles, and the outer layer becomes the nervous system, skin and hair.

The mother: There are no visible or obvious physical changes in the mother. This week, however, the mother is probably expecting her period, and if it does not come she will likely suspect that she is pregnant. Over the past week the mother may have experienced some light spotting, which is a common occurrence as the embryo implants itself in the uterus.

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