All About Pregnancy

In 1994, the live birth rate in the United States was 3,952,767, or 15.2/1,000 women. The unintended pregnancy rate during the same year was 48 percent of all pregnancies. Of the unintended pregnancies, 47 percent resulted in abortion, 40 percent in live births and 13 percent in miscarriages. The impaired ability to get pregnant was 10.2 percent in 1994, as reported by the National Center for Health Statistics.

Understanding Your Body:

The Female Reproductive System
The female reproductive system consists of those organs that allow for procreation. These include the ovaries, fallopian tubes, uterus and vagina. They create an environment suitable for the delivery of sperm to a mature egg, they allow fertilization to occur, and they provide nutrition for the growing fetus.

During their reproductive years (the time in a woman’s life lasting from puberty to menopause when she can have a baby), healthy women have monthly rhythmic changes, called the menstrual cycle, which are influenced by female hormones estrogen and progesterone. The menstrual cycle is about 28 days, although it can be several days longer or shorter, even in normal situations.

The menstrual cycle can be divided into two halves. During the first half (first 14 days) of the cycle, called the follicular phase (proliferative phase), the ova or eggs develop inside the ovary in small fluid-filled spaces called follicles. Usually just one of the follicles “matures” and grows in size to be between one-half inch and one inch. Also, during the later half of this phase, the lining of the uterus, or endometrium, builds up in preparation for reception of a fertilized egg.

Around the 14th day of a 28-day menstrual cycle, the mature follicle ruptures and the ovum is released from the ovary in a process called ovulation, and begins its journey to the uterus after being swept up by the fimbria, or fingers, of the fallopian tubes. If sexual intercouse occurs around the time of ovulation, sperm travel through the vagina and into the uterus via the cervix (the opening of the uterus into the vagina). Sperm then ascend in the uterus to enter the fallopian tubes where a single sperm may fertilize the egg. It then takes about five days for the fertilized egg to implant within the lining of the uterus, or endometrium.

The second half of the menstrual cycle (the last 14 days), the luteal phase (also known as the secretory phase) is characterized by the development of a corpus luteum (the empty follicle following ovulation and the cells surrounding it). The corpus luteum secretes large quantities of progesterone and estrogen which continue the maturation process and maintenance of the uterine wall. The uterus will be the home to the developing baby throughout the pregnancy.

If the ovum is not fertilized by sperm, then the hormones estrogen and progesterone rapidly diminish, and menstruation (bleeding from the uterus through the vagina) begins. A new menstrual cycle then begins and the process described above is repeated.