In this color 3-D scan of the human brain, the green central structure is the hypothalamus. This controls emotions and body temperature, and releases chemicals that regulate the release of hormones from the pituitary gland (green circle at bottom).

Like many women, you may sometimes feel ruled by your hormones, and it helps to understand why they fluctuate.

The hormone build-up to ovulation starts right now in week one of your menstrual cycle. Your pituitary gland, which lies in the base of your brain, produces follicle-stimulating hormone (FSH). During your period, the level of FSH rises steadily, triggering the development of the follicles (around 15-20 each month) in each ovary. As well as containing each egg, the follicles produce estrogen.

The hormone estrogen circulates, affecting the pituitary gland and causing it to produce luteinizing hormone (LH)-this triggers ovulation (see This is Day 14 of your Menstrual Cycle). This week your estrogen levels are low and steady, but will rise dramatically later in your cycle.

Progesterone levels are low during your period, but start to rise several days afterward and stay high for the second part of the cycle. Under the influence of progesterone, the muscles in the cervix relax, easing open the cervical canal. Changes also affect the mucus, which becomes more fluid, so sperm find it easier to swim through. It is progesterone that enables the lining of the uterus to thicken in preparation for implantation of the fertilized egg.

Changes during the menstrual cycle

There are four hormones at work during the menstrual cycle: FSH (follicle-stimulating hormone) causes the egg follicles to start developing in the ovary; estrogen is produced by the developing egg and peaks just before ovulation; LH (luteinizing hormone) triggers ovulation; progesterone thickens the lining of the uterus.

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As A Matter Of Fact

Men get PMS too!

Scientists have confirmed there's a male version of PMS-Irritable Male Syndrome. Mood swings, temper tantrums, and loss of libido in men were found to be caused by falling levels of testosterone due to stress.

The Lowdown

Fertility rites

Rooted in folklore, these fertility tips require a leap of faith and a good sense of humor!

Use the moon.
Exponents of "lunaception" believe that women whose menstrual cycle aligns with the lunar cycle-so they menstruate during the new moon and ovulate when the moon is full-have more chance of conceiving. It's based on the theory that women's cycles are influenced by natural light.
Dance around the Maypole.
Maypoles are thought to herald the arrival of spring and celebrate fertility.