How to use the Rhythm/Calendar Method! March 07, 2006 7:52 AM
Here I am going to try to explain how the rhythm/calendar method is supposed to work.
I am taking this information from the book I own called A cooperative Method Of Natural Birth Control By: Margaret Nofziger
Later, I will also be making threads about the BBT Method and the Cervical Awareness Method
The Rhythm/Calendar Method:
The rhythm method alone is only 60-80% effective. If you only use the rhythm method, there is a good chance you will get pregnant!
This is one of the oldest methods for determining fertility and infertility. It is based on three things:
1) Ovulation occurs about 2 weeks before your period. Fourteen days is average but it can be 12-16 days before.
2) Sperm are usually able to fertilize for 3 days on average
3) The life of the egg is only 12 to 24 hours long
If you keep track of several of your periods (the more the better) you subtract 2 weeks from your very shortest cycle and find out just about when you ovulated in these short cycles. This tells you the earliest you are likely to ovulate in future cycles.
Then you subtract 2 weeks from your longest recorded cycle to know the latest you are likely to ovulate in future cycles.
Now you take the earliest recorded ovulation date and count back two more days in case you ovulate 16 days before instead of the average 14 and then count back 3 more days for the maximum lifespan of the sperm. Now you have your last safe infertile day according to your past cycles.
After establishing this you go to the cycle day of your latest recorded ovulation and add 2 more days, incase your ovulation comes 12 days before your next period instead of the usual 14. Then add 1 more day to account for the 24 hours that the egg could live for. This gives you your most infertile days after the egg is gone.
One of the most popular calendar method formulas is called Ogino’s formula which is:
Shortest minus 19 for early, pre-ovulation safe days
Longest minus 10 for late, post-ovulation safe days
Since we use the temperature method (BBT) to establish the safe day after ovulation we will not bother with the second half of the formula. We do not have to figure out when the latest possible safe day is because the BBT will tell us when ovulation has actually passed.
The purpose of the calendar method when using FAM is to help us establish safe early days. But the original formula of Ogino did have a small failure rate (a few pregnancies). So we use a modified early safe day rhythm formula of …….
Shortest minus 21
S-21= last day of the pre-ovulation phase
This new formula gives you 7 days leeway before your estimated time of ovulation.
5 Days for the very maximum sperm life and 2 extra days in case you ovulate 16 days earlier that your period instead of 14.
If your shortest recorded cycle was 28 days, you stop making love after day 7 because fertility begins on day 8
28-21=7 (as the last safe day)
If the shortest cycle was 32 days, you would stop after day 11 (fertility begins on day 12).
32-21=11 (as the last safe day)
The rhythm method is more reliable the more past cycles you are considering. If you never had a cycle shorter than, say, 28 days in the last few years, you could be fairly sure of infertility to day 7. But it is very strongly suggested that you use the cervical awareness method and pay close attention to your cervical fluid while using this method as well. If your fluid says you are fertile than you can not trust the rhythm method and must abstain, but if they both say you are infertile, then you should be safe.
Another thing to remember is that your cycles rhythm can change at times because of stress, illness, travel, and/or drugs (prescription or not). So if you suspect any of these things may be effecting you, you should abstain.
Another thing to note is that some do not think that the calendar method should be used at all. They think that you should use a strict method of abstaining the entire early part of your cycle and only having sex after it is established that ovulation has passed by the BBT and Cervical methods (this means a lot less sex).
But if considering a lot of past periods and using this method correctly (and along with the other 2 methods). You should not have a problem. It is your decision to make though.
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