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How to Calculate Safe Period to Avoid Pregnancy

Updated on April 20, 2016

How do you calculate or know the days or safe period when you can avoid getting pregnant?

Is it really possible for a girl to be sexually active but not get pregnant without using protection?

Here's some information for the many women who choose to use natural family planning strategies instead of other contraceptive methods.

When Am I Fertile?

Many girls/women (and their partners) ask about the safe time in a woman's monthly cycle when a couple can make love without fearing pregnancy.

The chances of an unwanted pregnancy is next to nil, provided that you make love only on 'safe' days. But the question is, how do you really know if you are on safe days or not?

Normally conception occurs halfway through the cycle; when ovulation (release of the female egg) takes place. However, it becomes difficult to know when exactly the egg is released from the ovary. Women can be considered fertile for a few days before and after the time ovulation occurs.

Having unprotected intercourse during the days you consider 'safe' can’t guarantee pregnancy not taking place. You can do your best to avoid pregnancy, but both partners should be aware there is always an element of risk.

Natural Family Planning

There are many different contraceptive options available to men and women, but some couples choose natural family planning.

To avoid pregnancy, the woman calculates when her egg is likely to be released by the ovary and abstains from intercourse for a ten to 14 day period when she is most fertile. Natural family planning requires discipline (by both the man and the woman during the fertile period.

The way to avoid pregnancy if you rely on timing is to only have sex on safe days, and make sure the woman is not exposed to sperm during the fertile period.

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How to Calculate Safe Days to Avoid Pregnancy

To calculate and know the safe period for making love and not getting pregnant, you need to understand the menstrual cycle.

If a woman is absolutely regular and never changes from a 28 day cycle, her unsafe days will be between Day 11 and Day 18. Therefore, she should only consider intercourse between Day 19 through to Day 10.

The menstrual cycle generally varies between 26 and 31 days from woman to woman and the safe period to avoid pregnancy should be calculated as below.

Any woman with an irregular cycle should take note of the length of each cycle over a 12 month period. Many women make a note in their diaries or calendars showing the first day of each period. Look back over the past 12 months and figure out how many days between each cycle. Remember to factor in the precise number of days in each month. Take your time and don't make mistakes.

Let's say, for example, your shortest cycle was 25 days and your longest cycle was 31 days.

The longest cycle days subtracted by 11 days gives the last day of the fertile period. So in our example, 31 days - 11days = Day 20.

The shortest cycle days subtracted by 19 days gives the first day of fertile period. i.e 25 days- 19 days = Day 6.

From the calculation above the unsafe period (the fertile period) to make love and get pregnant is 6th to 20th day of each menstrual cycle. So these are the days to AVOID sexual intercourse if you don't want to get pregnant..

To identify the shortest and longest period cycles you are required to make an observation and draw a conclusion from it. You should observe your periods for 12 months and determine the number of days between starting date and the next period after which you will be in a good position to identify or know the shortest and longest period cycles which will in turn help you in knowing the safe and unsafe periods for getting pregnant.

The calendar method is very risky for any woman who has short cycles, and those whose cycles are very irregular. It is therefore recommended to use other methods of contraception.

Temperature Method to Identify Ovulation and Avoid Pregnancy

It is possible to use a very accurate thermometer to help you identify exactly when you are ovulating. Many women use ovulation thermometers when they are deliberately trying to get pregnant, but an ovulation thermometer is also useful for women hoping to avoid pregnancy.

Using a thermometer will NOT tell you your 'safe' days. What it can do, however, is help you identify your ovulation cycle so you can avoid intercourse in the days before and after ovulation.

Your temperature change when ovulating is only very small so if you choose to include the temperature method in your natural family planning strategy, you must be diligent about using (and recording) the results.

Because your temperature variation will only differ by as little as 0.5 to 1 degree Fahrenheit (0.2 to 0.5 degrees Celcius) during ovulation, it is important to remember the following points.

  • Temperature must be taken by mouth (not armpit or forehead).
  • Taken in morning when you first wake, same time each day.
  • Before getting out of bed.
  • Before food or drink.
  • Thermometer left in place for 3 minutes (or until alarm sounds on automated thermometers.)
  • Record each morning's temperature on a chart so you can watch your cycle.

Your temperature may rise for reasons other than ovulation, for instance fever or infection. You should note these kind of events on your chart to avoid confusion when interpreting the results.

© 2012 Daniel Long


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