Why do the rules exist? (period rules)

Disclaimer: As with any time I write about the specifics of fertility awareness, I’ve gotta remind you that you MUST take a class or AT LEAST read a full book on the sympto-thermal method of fertility awareness to practice it properly. Reading blog posts and downloading an app does not cut it, kapish? 

This post is part of a series: Why do the rules exist? 

Essentially, when you are using the sympto-thermal method of fertility awareness you are doing a few things:

• Checking your fertility signs.
• Charting your fertility signs.
• Applying “rules” to those fertility signs so that you know when you are inside and outside of the fertile phase of your cycle.

Knowing why the rules exist is very important because it helps you understand what rules you should never ever break if you are very strictly trying to avoid pregnancy, and what you might not care about if you are a little more on the “umm… I kinda don’t want to get pregnant, but at the same time I don’t really mind if I do get pregnant”- side of the trying to avoid scale. It also helps you understand how your hormones and cycle work better, making you a better user of the method.

Today I want to discuss the period rules.

It was brought to my attention that during the “why do the rules exist?” series, I didn’t mention the period rules. D’oh, Hannah!

During your period is a special time because:

• It is BEFORE you ovulate in that particular cycle, meaning you should be watching for cervical fluid to determine fertility.
• You can’t determine whether you have cervical fluid or not most days of your period. Because uterine lining, people.

Because of that, you can not use the typical pre-ovulation dry day rules when you are on your period.

One option, and something that some methods do, is consider the heavy days of the period fertile. This is because during the heavy days you definitely can not tell if their is cervical fluid. So to be extra safe, those methods just treat it like they would cervical fluid: fertile.

However, the chances of cervical fluid in the first few days of your cycle is very very (very!) low. Not to mention ovulation rarely happens before cycle day 10 and if it does the egg and follicle are often not mature enough to make it a truly fertile cycle.

Which is why there are period rules separate from checking fertility signs (like cervical fluid) just for those days of bleeding that you can’t determine whether you have cervical fluid or not.

A VERY important note about these rules is that they only apply to a true period, meaning ovulation had to have happened in the previous cycle. If the last “cycle” was anovulatory the bleed is not a true period but a breakthrough bleed and is a completely different hormonal event.

So what can be used as an alternative to checking cervical fluid during your period? *dundundun*… A calculation. Gasp! This is because you absolutely can not check cervical fluid during that time, so if you want to use those days at all (remember, some methods do not), you have to base your fertility off of previous cycles.

Because the relative likelihood of fertility (meaning unprotected sex resulting in pregnancy) before cycle day 5, the first five days of your period can be considered safe for unprotected sex IF you meet a certain set of criteria including having had an ovulatory cycle previously (so you have to be charting to consider the period an infertile time), not being perimenopausal (because you can start having short cycles randomly as you become perimenopausal), and not having had previous cycles under XXX days (if you have had shorter cycles you could be prone to earlier ovulation).

Some people and methods will choose to use the rule, but have only the first 3 days considered safe if not all of the criteria is completely met.

The first 5/3 day rule (again, what you use depends on your method of choice and “risk factors”) has been studied as very effective (it is included in the wonderful sensiplan study done in 2007), and using it doesn’t result in more than a 0.4% failure rate.

Do you have questions about the period rule(s)? Let me know in the comments.