Menstrual cycle

Irregular periods or ovulation disorders, meaning that you ovulate infrequently or not at all, are a common reason for having difficulties conceiving. 

Phases of the menstrual cycle

The menstrual cycle is the process of ovulation and menstruation controlled by hormonal changes that a woman’s body goes through in order to prepare for pregnancy.

There are typically three phases in your monthly menstrual cycle, controlled by two types of hormones: follicle stimulating hormones (FSH) and luteinising hormones (LH). Your cycle could become irregular or cease if the hormonal balance is disturbed for any reason.

Phase 1: The Follicular Phase

Day 1 of your cycle is the first full day of bleeding. Your levels of progesterone and oestrogen will drop at the end of the previous cycle, sending a signal to the pituitary gland to increase production of follicle stimulating hormone (FSH). A number of follicles (tiny sacs of fluid containing eggs) develop within the ovaries in the days leading up to menstruation. The developing follicles cause the FSH production to decrease, until there is only enough to encourage continuing development of a single follicle - the dominant follicle. The dominant follicle secretes increasing oestrogen which in turn increases the thickness of the lining of the uterus (the endometrium) in preparation for pregnancy, and changes the cervical mucus so sperm can pass through it more freely.

Phase 2: Ovulation (release of the egg)

As the level of oestrogen increases, the pituitary releases a short-lived surge of luteinizing hormone (LH). This hormone triggers ovulation, causing the dominant follicle to mature and release the egg. As the egg is released, the far end of the fallopian tube moves across the ovary and sucks up the egg. For a few days before ovulation, the cervical mucus allows sperm to pass through the cervix and uterus to the fallopian tubes. The sperm can survive there for 2 to 3 days, awaiting arrival of the egg. The egg itself is generally only able to survive 24 hours at most before it must be fertilised by a single sperm. Fertilisation normally takes place in the widest part of the tube, near the ovary. A membrane called the zona pellucida surrounds the egg and hardens, forming a shell, after one sperm has penetrated it, so other sperm cannot enter. Once inside the egg the sperm releases its contents and fertilisation occurs. The fertilised egg starts to divide into cells, the number of cells doubling with each division, and becomes known as an embryo.

Phase 3: After ovulation

The follicle from which the egg was released now begins to make progesterone. This hormone enables the lining of the uterus to provide nutrition, and a site for the embryo to implant during pregnancy. The embryo moves along the fallopian tube and once it reaches the uterus, it hatches out of its shell about four days after fertilisation, and implants in the lining of the uterus. The embryo then starts to produce the pregnancy hormone, human chorionic gonadotrophin (hCG) – the hormone measured in pregnancy tests. The presence of this hormone drives the ovary to continue making oestrogen and progesterone to support the pregnancy. If fertilisation fails or does not take place, the absence of pregnancy hormone causes the ovary to stop making oestrogen and progesterone so that the levels fall. Without these hormones, the lining of the uterus breaks down and the next period starts.

Common menstrual cycle abnormalities and treatment


Amenorrhea is the absence of menstrual periods. The most common causes of amenorrhea are lifestyle factors such as stress, weight loss or weight gain or excessive exercise; or hormonal imbalances caused by an underactive thyroid gland, pituitary tumor or reproductive conditions such as PCOS, hyperprolactinemia and ovarian failure or early menopause. Treatment will depend on the underlying cause and may include diet and lifestyle changes, hormone replacement therapy or management of the underlying condition.


Anovulation is the failure of the ovary to release an oocyte (egg) and is a common cause of infertility. Women who don’t ovulate will often have irregular periods or no periods. Common causes of Anovulation include PCOS, obesity or low body weight, thyroid dysfunction, premature ovarian failure, low ovarian reserves or hyperprolactinemia. Treatment will depend on the cause but may include diet and lifestyles changes or simple fertility drugs such as Clomid to trigger ovulation.


Hyperprolactinemia refers to excess levels of prolactin in the blood. Prolactin is a hormone produced by the pituitary gland and is primarily responsible for lactation. Common causes of hyperprolactinemia include illness, medication, pituitary tumors, hyperthyroidism or PCOS. Symptoms of elevated levels of Prolactin in women are disruptions to the menstrual cycle including irregular periods or no periods and production of breast milk unassociated with pregnancy. A bloof Hyperprolactinemia can be treated with drugs to reduce prolactin levels or Clomid to induce ovulation.

Luteal phase defect

The luteal phase is a stage of the menstrual cycle between ovulation and before the start of a woman’s period. During this phase the lining of the uterus thickens to prepare for pregnancy. If you have a luteal phase defect, the lining of the uterus doesn’t develop properly due to insufficient levels of Progesterone. Symptoms can include short menstrual cycles, spotting, miscarriage and difficultly falling pregnant and can be linked to conditions such as Endometriosis, PCOS, thyroid disorders and hyperprolactinemia. Treatment includes ovulation inducing drugs such as Clomid or IVF.

When is the most fertile time in my cycle?

The most fertile days in your cycle are the days leading up to ovulation; this is referred to as your fertile window. The egg can survive for about 24 hours after ovulation, while sperm can survive for 2 -3 days in the fallopian tube. To give yourself the best chance of conceiving you should be having unprotected intercourse every 2 -3 days during your pregnancy window so sperm is already present in the fallopian tubes.

Calculate your fertile window…

How do I know when I ovulate?

Every woman is different and your cycle may vary from month to month. The time from the start of your period to ovulation could be as little as 8 days or as long as 18. The time from ovulation to menstruation is more consistent though typically 12 – 16 days.

To work out when you ovulate, subtract 14 days from the number of days in your cycle. Your cycle is the number of days from the start of your period to the start of your next period. So if your cycle is 28 days you can expect to ovulate on day 14.

You may also notice other symptoms of ovulation around that time, such as vaginal mucus, tender breasts or an increased libido.

We don’t recommend using temperature charting or hormone kits as they only indicate ovulation after it has happened, and you need to have intercourse before ovulation occurs. If you are concerned about your menstruation cycle there are tests you can undergo to see what is happening.

Note that from time to time your cycle may change due to illness or stress.

Calculate ovulation date & fertile window…

What if my cycles are irregular?

If your cycles are irregular or your cycle length varies from month to month it could be difficult to calculate your ovulation date and fertile window. Ovulation urine tests or ovulation cycle tracking may be useful and you should seek advice from a GP or fertility specialist. 

You may have learned about your menstrual cycle in high school, but who else needs a refresher? If you're trying to conceive, having an understanding of your menstrual cycle is a great first step. In the below video, Dr Kath Whitton, fertility specialist at IVFAustralia, explains the phases of the menstrual cycle and how to optimise timing for conception.

Understanding the menstrual cycle

Having trouble conceiving?

Up to 40% of all female fertility issues are ovulation related and most can be treated with lifestyle changes or simple fertility drugs.

If you experience irregularities in your menstrual cycle and have been trying to conceive for 12 months (6 months if you are over 35 years of age) you could consider booking an appointment with a fertility specialist.  

Appointments are available in the next couple of weeks and will cost approximately $150 for a couple after the Medicare rebate.