Your menstrual cycle is divided into three phases – the follicular phase, ovulation and the luteal phase. The first half of your menstrual cycle is known as the follicular phase. This is followed by ovulation and the luteal phase. The follicular phase of your cycle starts on the first day of menstruation (when you see red bleeding) and ends when you ovulate. Unlike the luteal phase of a woman’s cycle –otherwise known as the two week wait –which is consistently around 12-14 days long, the length of a woman’s follicular phase can vary from woman to woman and from month to month. The follicular phase is when you are waiting to ovulate and can take as little as 7 days or as long as 30 or 40 days.
At the beginning of your cycle, the lining of your uterus is nice and thin. If the egg released during your previous cycle is not fertilized, your estrogen and progesterone levels will begin to drop. When your period arrives, it is because your estrogen and progesterone levels are low, indicating to your body that it is time to start a new cycle. Your body will begin shedding the top layer of your endometrium (the lining of your uterus) to make way for a healthier new lining.
At the same time, your hormones are starting to prepare new eggs for ovulation. At the start of your cycle, triggered by the low estrogen and progesterone levels, your pituitary gland starts producing a hormone known as GnRH (gonadotropin releasing hormone). GnRH stimulates the production of FSH (follicle stimulating hormone) and LH (luteinizing hormone), a couple of other hormones involved in ovulation.
FSH is important because it tells your ovaries to start preparing follicles for ovulation. As FSH stimulates your follicles, they will begin maturing eggs inside of them. Each follicle contains an egg. As your cycle progresses one of the follicles will become the dominant follicle and the egg contained inside that follicle will be the one that is released during ovulation.
As the follicles mature, they release estrogen. Remember your cycle started out with low levels of estrogen. This release of estrogen from the follicles is how your body knows when it is time to ovulate. When your estrogen levels reach a certain point, this tells your body that the egg is mature and ready to be released. To make this happen, your body releases LH. LH surges just before ovulation and it does this when your estrogen levels get high enough. After your LH surges, you can expect to ovulate within 12-36 hours. Once you ovulate, the second half of your menstrual cycle begins – the luteal phase.