Table of contents:

Although it is a little more difficult to know exactly when the fertile period is in women who have irregular menstruation, it is possible to have an idea of what the most fertile days of the month may be, taking into account the last 3 menstrual cycles or the evaluation of the duration of the cycle in the last year.
For this, it is important that the woman writes down the day of each cycle in which menstruation occurred, in order to know how many days she had each cycle, to be able to calculate the most fertile days.
However, as the cycle is irregular, the fertile period identified through the calculations may vary and, therefore, it is important that the gynecologist is consulted, in addition to being attentive to the indicative signs of fertile period, such as increased body temperature and increased vaginal secretion, and perform an ovulation test.

How to calculate
Calculating the fertile period in an irregular cycle can be more complicated, since ovulation and menstruation can happen at different times and, therefore, it is important that the gynecologist is consulted for a more accurate assessment..
Nevertheless, some popular forms of calculations can help to get an idea of the fertile period, but they should not be considered as absolute truths:
1. Average of the last three months
To calculate the fertile period, the woman must take into account the last 3 cycles and note the days on which the first day of menstruation occurred, determine the interval between these days and calculate the average between them.
For example, if the time interval between 3 periods was 33 days, 37 days and 35 days, this gives an average of 35 days, which will be the average duration of the menstrual cycle (to do this, just add the number of days of the 3 cycles and divide by 3).
After that, 35 must subtract 14 days, which gives 21, which means that ovulation occurs on the 21st day. In this case, between one period and another, the most fertile days will be 3 days before and 3 days after ovulation, that is, between day 18 and day 24 after the first day of menstruation. However, as the cycle is irregular, the period can be variable.
2. Annual cycle
In this case, the cycle duration must be recorded in each month, so that, after 1 year, it is possible to identify the longest cycle and the shortest cycle. Then subtract 18 from the longest cycle and 11 from the shortest cycle.
For example, the longest cycle lasted 36 days and the shortest 20 days. Thus, 36 - 18=18 and 20 - 11=9 should be done, which is indicative that the fertile period should be between the 9th and 18th day of the cycle. However, since the cycle is irregular, this period can be variable.
How to know your fertile period
To know the fertile period in the irregular menstrual cycle, it is important to be aware of some signs that may arise during this period, such as increased vaginal secretion, increased body temperature, increased appetite and libido and mood swings, for example. See more about fertile period signs.
After the appearance of these signs, it is interesting to perform an ovulation test, which can be purchased at pharmacies and which aims to check the concentration of the LH hormone in the blood, which is increased during this period. Understand how the ovulation test is done and how it works.
To increase the chances of getting pregnant, in addition to performing the ovulation test to know the fertile period and having sex during this period, it may be indicated to have sex at least every 3 days throughout month, especially on days when you can identify the signs of the fertile period.
How to protect yourself
For those who have an irregular cycle, the best strategy to avoid unwanted pregnancy is to take the contraceptive pill that will regulate the flow days, remembering to still use a condom in every relationship to protect yourself from infections as well sexually transmitted.