Pregnancy is an exciting time. Women who are trying to conceive or who have recently discovered that they are pregnant are often curious about the first month of prenatal development. The first month of pregnancy sets up the basic formation of all of the developing baby's future organs, tissues and systems that will support its growth while in utero.
Timing
Because of the way pregnancy is dated by doctors, the first two weeks of pregnancy are actually before conception. Doctors count a pregnancy as beginning at the date of the last menstrual period, which occurs about two weeks before ovulation, says the Mayo Clinic. During the two weeks after ovulation, most women are unaware that they have conceived, so the first month of pregnancy is typically unacknowledged by the woman.
Fertilization
Fertilization occurs in what is considered the second week of pregnancy. Fertilization takes place in the fallopian tubes when the sperm meets the egg traveling downward through the tubes to the uterus. This meeting of egg and sperm actually takes place a few minutes to a few days after sexual intercourse. Fertilization begins the development of the embryo that will lead to a baby.
Cell Division
The developing embryo undergoes a series of divisions after fertilization, The cells cleave again and again to become a mass of cells called a blastula. The blastula then becomes hollow and the cells begin to form layers on the inside of the blastula surface.
Cell Layers
After the blastula stage, the outer layers of cells start to differentiate into the amniotic sac and placenta. A small section of cells in the inner surface of the blastula separate into three layers, which will become different parts of the embryo, as described by the Child Development Institute's "Approximate Timetable of Prenatal Development." The inner layer is the ectoderm, which forms the nervous system and sensory organs. The mesoderm is the middle layer, which forms the muscular and skeletal systems. The outer layer is the endoderm, which will eventually become the digestive tract and glands.
Implantation
When the blastula arrives in the uterus after having traveled down the fallopian tubes it implants into the uterus. At this time, the cells that will grow into the embryo distinguish themselves from those that will become the placenta and other supporting tissues.
Embryo
At the end of the first month of gestation, the fertilized egg becomes an embryo. At this point, it is tiny, only about 1/4-inch in length, according to Sutter Health, a Northern California-based network of hospitals and physicians. The embryo is curved into a crescent shape. It contains, however, all of the basic cells needed to grow all of the fetal organs over the next few months. The tiny developing heart has begun to beat inside the embryonic body.
Concerns
Because most women who are pregnant do not become aware of the pregnancy until well into the second month, the first month typically passes without notice. All of the major systems of the future fetus, however, can be affected by things that occur during this time. It is important for women who might become pregnant to get an adequate intake of vitamins, especially folic acid, and to avoid smoking and drinking which could harm the developing embryo.
