Women’s cycle lengths vary, and the most common cycle length is somewhere between 23 and 35 days. Any variation in menstrual cycle length that does occur is more likely to be during the part of the cycle before you ovulate (which is called the follicular phase). For most women, the length of time between ovulation (when an egg is released from the ovary) and their monthly period is between 12 to 16 days (this is called the luteal phase).
The menstrual cycle
The first day of your menstrual cycle is the first day of your period (day 1). The period usually then lasts anything from 3 to 7 days. You’ll probably find that if you get any period pains, they’ll be at their worst in the first few days of your period. This is because the hormones in your body are causing your womb to actively shed the lining that was built up in the previous menstrual cycle.
Preparing for ovulation
At the beginning of your cycle follicle-stimulating hormone (FSH) is produced by the pituitary gland in your brain. This is the main hormone involved in stimulating your ovaries to produce mature eggs. Follicles are the fluid-filled cavities in your ovaries. Each follicle contains one undeveloped egg. The FSH stimulates a number of follicles to develop and start to produce the hormone estrogen. Your level of estrogen is at its lowest on the first day of your period. From then on, it starts to increase as the follicles grow.
Now while a number of follicles initially begin to develop, normally one follicle becomes “dominant” and this egg matures within the enlarging follicle. At the same time, the increasing amount of estrogen in your body makes sure that the lining of your womb is thickening with nutrients and blood. This is so that if you do get pregnant, the fertilised egg will have all the nutrients and support it needs to grow. High estrogen levels are also associated with the appearance of ‘sperm-friendly’ mucus (or, to give it its technical name, fertile cervical mucus). You may notice this as a thin, slippery discharge that may be cloudy white. Sperm can swim more easily through this mucus and can survive in it for several days.