Being aware of your menstrual cycle and the changes in your body that happen during this time can be key to helping you plan a pregnancy, or avoid pregnancy. During the menstrual cycle (average 28 days), there are two parts: before ovulation and after ovulation.

Day 1 starts with the first day of your period. Usually by Day 7, a woman's eggs prepare to be fertilized by sperm. Between Day 7 and 11, the lining of the uterus begins thickening, waiting for a fertilized egg to implant there. Around Day 14 , hormones cause the egg that is most ripe to be released, a process called ovulation. The egg travels down the fallopian tube towards the uterus. If a sperm unites with the egg here, the egg will attach to the lining of the uterus, and pregnancy occurs.

If the egg is not fertilized, it will break apart. Around Day 25 when hormone levels drop, it will be shed from the body with the lining of the uterus as a menstrual period.

The first part of the menstrual cycle is different in every woman, varying from 13 to 20 days long. This is the most important part of the cycle to learn about, since this is when ovulation and pregnancy occurs. After ovulation, every woman (unless she has a health problem that affects her periods) will have a period within 14 to 16 days.

Charting Your Fertility Pattern

Knowing when you're most fertile will help you plan for your pregnancy. There are three ways you can keep track of your fertile times.

They are:

Tracking Basal body temperature - Basal body temperature (BBT) is your temperature at rest as soon as you awake in the morning. A woman's BBT rises slightly with ovulation. So by recording this temperature daily for several months you'll be able to predict your most fertile days.

BBT differs slightly from woman to woman. Anywhere from 96 to 98 degrees is average before ovulation. After ovulation most women have a temperature between 97 and 99 degrees. The rise in temperature can be a sudden jump or a gradual climb over a few days.

Usually a woman's basal body temperature rises by only 0.4 to 0.8 degrees Fahrenheit. To detect this tiny change, women must use a basal body thermometer. These thermometers are very sensitive. Most pharmacies sell them for around $10. You then record your temperature on a special chart.

The rise in temperature doesn't show exactly when the egg is released. But almost all women have ovulated within three days after their temperatures spike. Body temperature stays at the higher level until your period starts.

You are most fertile and most likely to get pregnant:

• two to three days before your temperature hits the highest point (ovulation), and - 12 to 24 hours after ovulation.

A man's sperm can live for up to three days in a woman's body. The sperm can fertilize an egg at any point during that time. So if you make love a few days before ovulation you are likely to conceive. Many things can affect BBT. To get the most accurate chart you should take your temperature every morning at about the same time.

Things that can alter your temperature include: - drinking alcohol the night before - smoking cigarettes the night before - getting a poor night's sleep - having a fever - doing anything in the morning before you take your temperature, including going to the bathroom and talking on the phone.

Using A Fertility Calendar - This involves keeping a written record of each menstrual cycle on a fertility calendar. The first day of your period is Day 1. Circle Day 1 on the fertility calendar. Do this for 8-12 months so you know how many days are in your cycle. The length of your cycle may vary from month to month. So write down the total number of days it lasts each time. To find out the first day when you are most fertile, check your list for the cycle with the fewest days. Then subtract 18 from that number. Take this new number and count ahead that many days on the calendar. Draw an X through this date. The X marks the first day you're likely to be fertile. To find out the last day when you are fertile, subtract 11 days from your longest cycle and draw an X through this date. This method always should be used with other fertility awareness methods, especially if your cycles are not always the same lengths.

Checking Your Cervical Mucus - This involves being aware of the changes in your cervical mucus throughout the month. The hormones that control the menstrual cycle also change the kind and amount of mucus you have before and during ovulation. Right after your period, there are usually few days when there is no mucus present or "dry days." As the egg starts to mature, mucus increases in the vagina, appears at the vaginal opening, and is white or yellow and cloudy and sticky. The greatest amount of mucus appears just before ovulation. During these "wet days" it becomes clear and slippery, like raw egg whites. Sometimes it can be stretched apart. This is when you are most fertile.

About four days after the wet days begin the mucus changes again. There will be much less and it becomes sticky and cloudy. You might have a few more dry days before your period returns. Record changes in your mucus in your fertility calendar. Label the days, "Sticky," "Dry," or "Wet." You are most fertile at the first sign of wetness after your period or a day or two before wetness begins. This method is less reliable for some women. Women who are breastfeeding, taking hormonal contraceptives, using feminine hygiene products, have vaginitis or sexually transmitted diseases, or have had surgery on the cervix should not rely on this method.

To most effectively track your fertility, use a fertility calendar to track your Basal Body Temperature and Cervical Mucus each month.