The Female Cycle

The Uterus

The uterus is located in the lower abdomen between the bladder and the rectum.  The uterus is also called the womb.  It is a muscular chamber that is the size of a pear.  The lower, narrow end of the uterus is the cervix.  When a woman conceives (becomes pregnant) the embryo and then fetus grows in the uterus until birth.

The cervix is the opening of the uterus through which sperm enters to fertilize an egg, and through which a fetus leaves the uterus during a vaginal delivery.

The ovaries are two almond-sized structures located on either side of the uterus.  Each holds thousands of tiny egg follicles-clusters of cells that contain an immature egg at their centers.  The ovaries also produce hormones needed to reproduce.

The fallopian tubes connect the ovaries and the uterus.  About four inches long, they each begin at an opening on either side of the uterus and end in a funnel that surrounds (but doesn’t touch) each ovary.

Ovulation & Conception

Once a month, the lining of the uterus begins to thicken in preparation to receive and nourish a fertilized egg.  At the same time, several egg follicles begin to mature within the ovary, but usually only one develops fully, with a mature egg inside.

The mature egg moves to the surface of the ovary and the follicle opens to release the egg into the fallopian tube.  This process is called ovulation.  Over the next few days the sides of the fallopian tube squeeze periodically to push the egg to the uterus.

If the egg in not fertilized during this critical time, it will disintegrate in the uterus.  Consequently, since the thickened uterine lining is no longer needed, it will be shed over a period of 2 to 8 days.  This discharge, containing blood, cells and other secretions is called menstrual flow, or a period.  The time interval from one period to the next is called the menstrual cycle and can be 21-31 days long.

Just after ovulation, while the egg is on its way toward the uterus, it may be fertilized by a man’s sperm, which is deposited during sexual intercourse.  Several million sperm can be contained in the semen released from the penis, but only one sperm must reach the egg, usually while it is still in the fallopian tube, for a pregnancy to occur.  This process is called conception.

Once fertilized, the egg begins to develop rapidly and becomes a cluster of 13-32 cells, which takes a few days to travel down the fallopian tube and into the uterus.  By the eight day, this cluster of cells, called a blastocyst, has increased in size to hundreds of cells and has begun to implant into the uterine lining.  After the blastocyst is implanted in the uterus it is then referred to as an embryo until the eigth week of pregnancy.  After the eight week of pregnancy the embryo is referred to as a fetus until birth.

If pregnancy occurs, and the egg is fertilized and implanted in the uterus, the thick lining of the uterus is not shed (your period), but used to nourish the fertilized egg. This is why you will miss your period if you become pregnant.

When am I most likely to conceive?

Every woman’s cycle is different.  It is possible to conceive on almost any day in your cycle.  For women with 28 day cycles, ovulation is likely to occur 14 days before the next menstrual period is expected.  Typically, you can count 14 days from the first day of your last period, three days prior to the 14th day, and three days past the 14th day and these seven days are the most likely days to conceive.  However, as stated above, conception can occur on almost any day in your cycle, so be sure to talk to your health care provider about contraception.

Sperm can survive in the fallopian tubes for 2 or 3 days. Although the egg may be in the fallopian tube for 2 or 3 days, the fertile period usually ends by the time the unfertilized egg reaches the uterus.  Remember that your fertile period may vary from the norm and may even change from cycle to cycle.  If you are interested in determining your own cycle, consult with your heath care provider.