## The duration of the menstrual cycle

The average cycle length is from 21 to 35 days. However, in some women, the interval between periods is less than 21 or more than 35 days, but this is not always a deviation from the norm. To ensure no diseases causing disturbances of the cycle, women with short or too long a cycle needs to be examined by a gynecologist. It should be noted that an irregular cycle can be a consequence of overwork, stress, weight changes. Also deviations from the normal schedule produce hormones and changing climatic zones (e.g., a trip abroad during the holidays).

## How to calculate your menstrual cycle

In gynecology it is believed that the beginning of the menstrual cycle is the first day of menstruation, and it ends the day before the first day of the next menstruation. First you should consider even the day of bleeding is negligible.

Conventionally, the entire cycle is divided into "safe" and "dangerous" (fertile) days. On the first and second phase of the cycle have a safe period, and the third phase starts on ovulation, which lasts several days and is replaced by a fourth stage, preceding the beginning of the next menstruation.

For the correct calculation of the cycle must be at least six months to conduct a menstrual calendar, noting it is the beginning and end of menstruation. On the basis of the calendar is determined by the minimum and maximum duration of the cycle. The knowledge of these data will be required in order to determine the ovulation period and the so-called safe period.

## Determination of fertile days

Analyzing the calendar data for the six months, you need to choose the shortest and the longest cycle. For example, the minimum cycle is 28 days and maximum 32 days. Then from the number of days a short cycle you need to take 18, and of the long — 11. That is, 28-18=10 and 32-11=21. The result is that the days cycle with 10 to 21 optimal for conception. Therefore, women who do not take birth control pills to avoid unwanted pregnancy these days, you need to use reliable contraception.

This method of calculation only works in the case when the loop is relatively stable, and the intervals between periods are always about the same. If the cycle varies, for example, from 21 to 30 days, the calendar method for determining ovulation will be inaccurate.