The Female Reproductive System

     Women are born with about 400,000 eggs, they are stored in two small organs known as the ovaries.  During a woman's reproductive years, she usually releases a single mature egg, or ovum, each month as part of her menstrual cycle.  In addition to producing a mature egg, the ovaries produce the female hormones estrogen and progesterone.

     The eggs develop and mature inside follicles, which are tiny fluid-filled sacs that exist in each ovary.  At midcycle, one egg is released from a follicle in a process known as ovulation.  After the egg travels along one of the fallopian tubes toward the uterus, it is ready for fertilization by the man's sperm.  If a sperm penetrates the egg, fertilization occurs.  The fertilized egg then implants itself into the lining of the uterus, where it will gain nourishment as it grows.

     The uterus is the muscular organ where a fertilized egg, or embryo, attaches and develops.  it is about the size and shape of a pear and is lined with a rich and nourishing mucous membrane called the endometrium.  The vagina is the passage that leads from the outside of the body to the cervix, which is the opening of the uterus.

     Normal anatomy and regular menstrual cycles in the female are important factors in establishing fertility.  Monthly changes in a woman's hormone levels control the sequence of events.  To help understand the process a little better, it is important to understand the menstrual cycle and the hormones involved.

Understanding the Menstrual Cycle

     The menstrual cycle refers to the maturing and release of an egg and tot he preparation of the uterus to receive and nurture an embryo.  The typical cycle takes approximately 28 to 32 days and is divided into three distinct phases.  On the first day of the cycle, when menstruation begins, the uterus sheds its lining from the previous cycle.

Follicular Phase - Day 1 to about Day 13

     During this phase, the body releases a hormone known as follicle-stimulating hormone (FSH).  FSH stimulates the development of a follicle, which contains the maturing egg.  The follicle also secretes estrogen, which produces midcycle changes in the cervical mucus.  These changes help prepare the cervical mucus to receive and nourish sperm from the man.

Ovulatory Phase - Around Day 14

     The ovulatory phase begins with the level of hormone called luteinizing hormone (LH) dramatically increases, or surges.  LH causes the follicle to break open and release its egg into the fallopian tube.  This process is known as ovulation and lasts approximately 24 hours.

Luteal Phase -- Day 15 to Day 28    

     After ovulation occurs, the luteal phase begins.  During the luteal phase, the follicle that produced the egg becomes a functioning gland called the corpus luteum.  The corpus luteum produces progesterone, which prepares the uterus with the rich lining needed for implantation of the fertilized egg (embryo).

The Best Time for Fertilization and Pregnancy

     A woman's fertile time is around midcycle when ovulation occurs -- on or about the 14th day after the first day of the period.  Unlike the rest of the monthly cycle, cervical mucus is receptive to sperm around the time of ovulation.  When a couple is having intercourse during this time, sperm swim into the cervical mucus.  Gradually, sperm swim into the uterus and along the fallopian tube, where the egg and sperm unite.  The egg can be fertilized fro about 24 to 48 hours after it is released from the follicle.

  The fertilized egg, or embryo, travels back through the fallopian tube toward the uterus.  Once inside the uterus, the embryo implants itself into the lining on about the 20th day of the cycle.  The corpus luteum can sense the pregnancy and will continue to produce progesterone, thus preserving the uterine lining and pregnancy.

    If fertilization does not occur, the egg passes through the uterus, and the corpus luteum will cease to function on about day 26.  The uterus will then break down and shed its lining several days later, and the next menstrual period begins.

Common Causes of Female Infertility

Abnormal Ovulation

     Abnormal Ovulation, often referred to as hypothalamic pituitary dysfunction, results in irregular or absent menstrual periods.  The vast majority of the time, this is caused by a hormonal imbalance due to improper coordination and communication between the part of the brain called the hypothalamus and the pituitary gland.  Together, these two organs causes the release of hormones into the bloodstream.  In many cases, abnormal ovulation can be successfully treated with hormonal therapy.  Problems with ovulation may also be associated with extremely low body weight or with being overweight, as well as any significant change in weight (loss or gain).

Blocked Fallopian Tubes

     Blocked or damaged fallopian tubes may interfere with the egg and sperm uniting.  Blockage may also negatively affect embryo development and implantation in the uterus.  They can be caused by a previous infection, such as an earlier episode of pelvic inflammatory disease (PID), or abdominal surgery.  Often, there are no symptoms associated with blocked or damaged fallopian tubes.  Treatment of tubal problems or pelvic scarring may require specialized surgery, depending on each woman's situation.

Endometriosis

     Every month the lining of the uterus, the endometrium, thickens in preparation for the implantation of an embryo.  Sometimes the endometrial cells will migrate from their normal location and attach to the ovaries and other pelvic organs.  This is called endometriosis and may cause infertility. 

Cervical Problems

     When the body is not ovulating, cervical mucus helps prevent infection by killing bacteria.   However, at the time of ovulation cervical mucus should change to encourage sperm survival.  Cervical problems may be related to consistency of the cervical mucus or cervical anatomy, which will not allow the sperm to enter the uterus.

Age

     Fertility levels decrease with age, especially in women.  Maximum fertility for women occurs between the ages of 15 and 24.  Many couples delay starting a family until they are in their 30's or 40's.  About one third of women who defer pregnancy until their mid-30's will have a problem becoming pregnant, and at least half of all women over age 40 will have difficulties.  Because the likelihood of conceiving declines with age, women over age 35 should wait no more than six months before seeking help if they suspect a possible problem.