Female Biology

A woman is born with all the eggs she'll ever have.

A woman is born with over a million eggs in her ovaries. By the time she reaches puberty, she'll have about 300,000 left. Of these eggs, only about 300 will mature and be released during her reproductive years.[1]

All of her eggs are stored in her ovaries. The hormones she needs for menstruation and to become pregnant are produced by her hypothalamus, pituitary, and ovaries.

It's all about the cycle.

A woman's monthly menstrual cycle drives her ability to conceive. The cycle begins on the first day of a woman's period and typically lasts about 28 days. The first day begins not when she is spotting, but when she experiences regular flow.

The cycle is then divided into two distinct phases:

Follicular Phase: days 1 - 14

During the first 13 days of her cycle, follicle stimulating hormone (FSH) stimulates the development of a fluid-filled sac called a follicle in one of her ovaries. This follicle then produces a single mature egg. While this is happening, the follicle secretes estrogen which prepares the cervical mucus at the entrance of her uterus to receive sperm. The endometrium (lining of the uterus) also begins to thicken during this phase.

A surge in luteinizing hormone (LH) facilitates the final step of the maturation of the egg and, on about the 14th day, triggers ovulation. The egg is released from one of her ovaries and travels down a fallopian tube. When a couple has intercourse, a man's sperm attempts to swim past the cervical mucus and into the fallopian tube where it can fertilize the egg. The optimal days for conception are the ones just before and after ovulation, generally days 11 – 17.

Luteal Phase: days 15 - 28

Following ovulation, the hormones progesterone and estrogen develop and maintain the endometrium for receiving a fertilized egg. If the egg is fertilized, the embryo travels down the fallopian tubes to implant itself in the endometrium on about the 20th day of the cycle. Here it will develop into a fetus. If the egg isn't fertilized, it passes through a woman's body on about the 26th day. The uterus then sheds its lining and a woman's period begins, starting a new menstrual cycle.

It is important to realize that not all women have 28-day cycles. Therefore, the specific days of your Follicular and Luteal phases may be different. For more information, speak to your healthcare provider or call Fertility LifeLines™ at 1-866-LETS-TRY (1-866-538-7879).

The critical role that hormones play.

If this sounds complex, it is. Each step in the cycle is controlled by hormones that must generally be produced in the correct amounts, at the right times, in order for a woman to conceive. Any interruptions can disrupt your ability to conceive. Many factors may play a role in reducing fertility such as age and lifestyle choices.

If you'd like to learn more...

If you have concerns about your fertility, you should talk to your healthcare provider. If you make an appointment, read some suggested questions that you might want to ask your healthcare provider.