A simple guide to the Menstrual cycle
Tip of the Month: August 2010

Women have them every Month. Men have to put up with them (and us) every Month. Yet how many of us actually know what goes on in the body during the female monthly menstrual cycle?

The menstrual cycle has been split by scientists into three distinct phases. Stage 1 the follicular phase, stage 2 the ovulatery phase and stage 3 the luteal phase.

Stage 1: The Follicular Phase (before the egg is released)

This phase officially starts on day 1 of menstrual bleeding and can last between 13-14 days. At the beginning of this phase the endometrium (this is the lining of the uterus) is thick and full of nutrients as it is ready to nourish a fertilized embryo. However, if an egg has not been fertilized then the top layers of the endometrium are shed by the body which causes our Monthly menstrual bleeding.

During this phase the pituitary gland starts to increases it production of follicle-stimulating hormones. These hormones stimulate the growth of anywhere between 3-10 follicles, all of which contain an egg. As you will see later on only one of these eggs (the dominant one) will get released into the uterus.

Hormonal levels and changes during the follicular phase:

1. Luteinizing hormones – low until end of phase
2. Follicle-stimulating hormones – starts to increase
3. Oestrogen – levels decrease
4. Progesterone – levels are low (as an egg has not been fertilized)

Stage 2: The Ovulatery Phase (the egg release)

This phase begins when the luteinizing hormones surge. These hormones stimulate the dominant follicle to bulge from the surface of the ovary and rupture releasing the egg into the uterus.

Hormonal levels and changes during the ovulatery phase:

1. Luteinizing hormones dramatically increase – stimulates ovulation 16-32 hours after hormone surge
2. Follicle-stimulating hormones slightly increase (the reason for this is still not known)
3. Oestrogen - peaks during the luteinizing hormone surge
4. Progesterone - levels start to increase

Stage 3: The Luteal Phase (after egg release)

This phase begins after ovulation and lasts for around 14 days.

The follicle that ruptured during the ovulatery phase begins to close forming a structure called a corpus luteum. This corpus luteum is really important as it releases increasing quantities of progesterone into the uterus preparing it for fertilization. Progesterone readies the uterus by:

• thickening the endometrium (the hormone oestrogen also helps this process to occur)
• thickening the mucus in the cervix to stop sperm and bacteria entering the uterus
• increasing the core temperature of the body
• dilating the milk ducts in the breast which can in some cases make the breasts quite tender.

If an egg is not fertilized then the corps luteum will remain active for 14 days before fully degenerating spurring the follicular stage and our Monthly cycle to start all over again.

Hormonal levels and changes during the luteal phase:

1. Luteinizing hormones - decrease
2. Follicle-stimulating hormones - decrease
3. Oestrogen – remains high throughout this phase

Progesterone – continue to increase unless egg is not fertilized & then it starts to decrease.