The rhythm method is one of the oldest means of charting fertility and is often used for family planning by those who are unable to use alternative methods (such as Catholics). It simply involves monitoring your menstrual cycle and establishing the patterns of fertility and infertility throughout.

The menstrual cycle is categorised into several phases and just as cycle length differs between women, the duration of each menstrual phase varies also. The first is known as the 'menstrual phase' as day 1 of each cycle is classified by the first day of menstruation; this typically lasts between 3 and 5 days and is classified as a period of relative infertility.

The second phase is the 'follicular phase' and it is during this time when the body prepares itself for a potential pregnancy. The follicular phase typically lasts 8 or 9 days, however this varies greatly between women and often changes on a monthly basis. You become increasingly fertile as the follicular phase progresses with the last 5 days being the most likely to facilitate pregnancy.

Ovulation occurs around day 14 but again this varies widely for each individual. Fertility levels remain high for 1 or 2 days after ovulation has occurred and then begin to tail off. The final phase before the cycle recommences is the 'luteal phase', the average length of this phase is 14 days. Although the exact length of this phase varies between women, the duration for any individual is likely to be the same each month (i.e. always 13 days).

Although the rhythm method is not considered an accurate way of preventing pregnancy due to variation in phase length, by establishing your monthly menstrual routine you can begin to work out when you are likely to be most fertile. In order to establish the average length of your cycle you should make a note of the first day of your period for several months (6 months is advisable) and count the number of days in between; the average duration will be the typical length of your cycle. After you have established the average number of days in your cycle you can begin to work out when you are most likely to be fertile.

Use of the rhythm method in conjunction with more indicative predictors such as charting BBT (basal body temperature) and cervical mucus on a monthly basis will be able to give you a better idea of when your fertility peak falls and enable you to work out the best time to try and conceive