Question

Why is the period between 10 and 17 days of the menstrual cycle called a fertile period?

Answer 1

In a menstrual cycle, there are four major phases that take place in a woman. The four phases are - menstruation, follicular phase, ovulatory phase, and luteal phase. The LH hormone usually induces ovulation around the 14th day of the menstrual cycle, but for safe calculation reasons, we take the range of probability as $14 \pm 3/4$ days.

Complete answer: In an average cycle of 28 days, ovulation is said to occur on the 14th day. This is because both the FSH (Follicular Stimulating Hormone) and LH (Luteinizing Hormone) attain a peak on the 14th day. This rapid secretion of the LH leading to its maximum level in the mid-cycle is known as the LH surge. This induces the rupture of the Graafian follicle. Due to this, the ovum is released out for fertilization.

However, the hormonal imbalance can cause the delayed or the early release of the ovum. Also, the length of the cycle varies from female to female. Thus, for the safe side, the fertile period is considered from day 10 to day 17 of the menstrual cycle. 3-4 days before ovulation and 3-4 days after ovulation, are all the fertile days. The length of the menstrual cycle varies from women to women. The 28 days is considered just the average. However, in some women, the cycle can be shorter than 28 days and for some women, it can be greater than that. So, the day of ovulation for a menstrual cycle is calculated as follows –
Day of ovulation = Number of days in a menstrual cycle – 14
The number of days in a menstrual cycle means the number of days between two consecutive menses.

Note: The number of days in the menstrual and the follicular phase are variable. However, the number of days is fixed for the luteal phase. A luteal phase always lasts only 14 days. And at the boundary of the luteal phase is ovulation. This means that after ovulation, the luteal phase begins. Thus, the above formula is achieved by subtracting the length of the luteal period from the number of days of the menstrual cycle.