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Fertility and Your Menstrual Cycle

June 10, 2008 - 7:30am
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Unless you are one of the few women who is able to get pregnant during the first month of trying, you would probably benefit by learning more about your menstrual cycle. Having a good understanding of your menstrual cycle can help you time intercourse and increase your chances of becoming pregnant.

Understanding Your Menstrual Cycle

On average, a woman’s menstrual cycle is 28 days long, but it can vary—from approximately 17-36 days. Day 1 of your menstrual cycle begins on the first day of your period. Between Day 7 and 11, the lining of your uterus begins to thicken, preparing for a fertilized egg to implant. Around Day 14 of a 28-day cycle, changes in hormones cause a mature egg to be released from an ovary and travel down a fallopian tube toward your uterus. It is here that a sperm may fertilize the egg, and if this occurs and the egg attaches to the lining of the uterus, pregnancy occurs.

When trying to get pregnant, it is helpful to know when the egg is released, as that is the best time to achieve a pregnancy. The table below describes four of the most common methods that can be used to track when you are most fertile each month.

Basal body temperature This method involves taking your basal body temperature (BBT) each morning at the same time before you get out of bed and recording it on a chart . For this method you will need to purchase a BBT thermometer at a drug store for about $10, since the thermometer must be accurate enough to detect temperature changes of at least 1/10 of a degree. During your menstrual cycle, your body temperature is lower (96-98ºF) until ovulation. On the day of ovulation, your temperature will rise between 0.4 and 0.8ºF, and remain at that level until your period starts. Once your temperature stays at this higher level (97-99ºF) for three days, it is likely that you ovulated. Your most fertile days are the 2-3 days before your temperature hits its highest point, and the 12-24 hours after you have ovulated. Since you may not see the temperature rise until the day after ovulation, this method is best used to track your ovulation pattern over the course of a few months and begin to learn how to predict when you will ovulate.
Calendar With the calendar method, you will use a calendar to track your menstrual cycle for 8-12 months. Circle Day 1 (the first day of your period) on the calendar. Since cycle lengths can vary, make a list of the number of days of your cycle each month (i.e., Day 1 through the day before your next period).
  • To find the first day when you are the most fertile, subtract 18 from your shortest cycle, and mark an X on your calendar on this day of each cycle. (For example, if your shortest cycle was 27 days, the first day you are the most fertile will be Day 9 of your cycle; 27-18=9.)
  • To find the last day you are fertile, subtract 11 from your longest cycle and draw an X through this date. (For example, if your longest cycle was 29 days, the last day you are fertile will be Day 18 of your cycle; 29-11=18.)
Since this method cannot pinpoint the exact day you ovulate, it should be used in combination with other methods.
Cervical mucusIf you use the cervical mucus method, you will track changes in your cervical mucus (the fluid at the opening of your cervix) during your cycle. Hormonal changes that control ovulation also affect the type and quantity of cervical mucus. Right after your period, there will be a few days of little or no mucus, known as “dry days.” As the egg starts to mature, the quantity of mucus increases, and is usually white or yellow and cloudy and sticky. Just before ovulation (the “wet days”), the greatest amount of mucus appears, and it will be clear, slippery, and sometimes stretchy, similar to raw egg whites. Again, your most fertile days are just before and just after ovulation.
Ovulation predictor kit There are a variety of ovulation prediction kits available in drug stores. These kits measure the amount of luteinizing hormone (LH) in your urine, and use this information to determine when you ovulate. There are two types of kits:
  • One type is used to measure LH for the days during your menstrual cycle you are most likely to be fertile (see the calendar method above). A package of 5-9 tests costs $15-$30, and you can expect to spend $15-$70 per month.
  • The other type of kit measures your LH level daily, and tells you when your fertility is low, high, and peak. These testing machines cost around $170, and a month’s worth of test strips cost about $50.


Fertility awareness and infertility. National Women’s Health Information Center website. Available at: http://www.womenshealth.gov/Pregnancy/infertility.cfm . Accessed August 3, 2005.


Healthy Pregnancy
National Women’s Health Information Center

Last reviewed May 2007 by Jeff Andrews, MD, FRCSC, FACOG

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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