Whenever we hear the term the ‘Rhythm method’ we're transported back through the years to a dark and airless classroom where a bespectacled elderly man droned in monotone on the subject of the contraceptive rhythm method to 20 excruciatingly embarrassed teenaged girls. Needless to say we didn’t absorb much of the information imparted in the class! Perhaps it’s better that we didn’t as the rhythm method isn’t a reliable means of contraception, nor a reliable way of predicting ovulation as an aid to conception.
The rhythm method uses the length of past cycles and the assumption that ovulation occurs fourteen days before the start of your period to predict future ovulation. The problems with this method are twofold. One, that the length of the average woman’s menstrual cycles can vary and two, that ovulation doesn’t necessarily occur fourteen days before your period starts.
Meanwhile in the real world...
Some women usually have regular periods and some women have irregular periods: a cycle length of between 24 and 36 days is considered ‘normal’. But even women with regular cycles may sometimes have delayed ovulation due to medical or environmental factors like illness, stress and travel. So even if you were to accurately work out what day you usually ovulate, there’s no guarantee that you’ll ovulate on the same day in your next cycle. If you only use past cycles to predict your future cycles then you may assume you’re safe by day 16 of your cycle when stress, travel, physical exertion or another factor may have delayed ovulation and you cannot be sure if you have entered your fertile phase or not.
Regardless of whether or not your period does arrive at the regular time, the rhythm method may predict an incorrect fertile phase by miscalculating the time of ovulation at 14 days before your period is expected. The second half of your cycle, the luteal phase, is usually regular for an individual but its length can vary from person to person – anything between 12 and 16 days is usual.
The rhythm method is a way of judging when you might get your period so as to prepare for it. It’s not a reliable method of contraception.
So does that mean natural family planning is out of the question?
No, far from it, there's more to natural family planning than the rhythm method. Charting several fertility signs such as your waking temperature, changes in cervical mucus and changes in cervical position will allow you to gain a far more accurate picture of when you may be most fertile, and confirm when ovulation has taken place for contraceptive purposes.
To track ovulation you can also use you can use ovulator prediction kits (OPKs), which test urine for luteinizing hormone (LH). Bear in mind that charting your temperature and other fertility signs will give you more information about your reproductive cycle than an OPK and will tell you when ovulation has actually taken place as well as when it may be approaching, which is important as you may have more than one surge of LH before ovulation actually occurs.