Understanding Ovulation Cycles

What is Ovulation?

Ovulation is the name of the process that happens once in every menstrual cycle when hormone changes trigger an ovary to release an egg. This usually happens 12 to 16 days before your next period starts. The eggs are contained in your ovaries. During the first part of each menstrual cycle, one of the eggs is being grown and matured.

As you approach ovulation, your body produces increasing amounts of a hormone called estrogen, which causes the lining of your uterus to thicken and helps create a sperm friendly environment. These high estrogen levels trigger a sudden increase in another hormone called LH (luteinising hormone). The so-called LH surge causes the release of the mature egg from the ovary – this is ovulation.

Ovulation normally occurs 24 to 36 hours after the LH surge, which is why the LH surge is a good predictor for peak fertility. The egg can only be fertilised for up to 24 hours after ovulation. If it isn’t fertilised the lining of the womb is shed (the egg is lost with it) and your period begins. This marks the start of the next menstrual cycle.

While an egg only survives for up to 24 hours, sperm can remain active for up to five days. It may therefore be surprising to learn that a couple can conceive through sexual intercourse four to five days before the egg is released.

The total ‘fertility window’, taking into account the lifetime of both the sperm and the egg, is about 6 days.

When does ovulation occur?

A woman’s menstrual cycle lasts between 28 and 32 days on average. The beginning of each cycle is considered to be the first day of her menstrual period (menses). Ovulation itself generally occurs between day 10 and day 19 of the menstrual cycle, or 12 to 16 days before the next period is due.

Young women will begin to menstruate – a time referred to as menarche – between the ages of 9-15, and during this time will ovulate and be able to become pregnant.

Ovulation typically stops after menopause around the age of 51. Ovulation still occurs during the time leading up to menopause, however, which is referred to as peri-menopause.

What are the phases of ovulation?

The entire ovulation phase is defined by a period of elevated hormones during the menstrual cycle. The process itself can be informally divided into three phases:

• Periovulatory (follicular phase): a layer of cells around the ovum begins to mucify (become more mucous-like) and expand, and the uterus lining begins to thicken.

• Ovulatory (ovulation phase): enzymes are secreted and form a hole (or stigma) that the ovum and its network of cells use to exit the follicle and eventually enter the fallopian tube. This is the period of fertility and usually lasts from 24 to 48 hours.

• Postovulatory (luteal phase): a hormone called LH or luteinizing hormone is secreted. A fertilized egg will be implanted into the womb, while an unfertilized egg slowly stops producing hormones. In addition, the lining of the uterus begins to break down and prepares to exit the body during menses.

How do you know you’re ovulating?

Women’s cycles can vary and are not always as regular as clockwork, so to know that you are ovulating and on which day of your cycle you are ovulating, observe your fertility signs throughout your cycle and record them on a chart.

The most accurate methods of working out when ovulation is about to occur are:

Keep an eye out for changes in your mucus. Around the time of ovulation, you may notice your vagina’s mucus is clear, slick and slippery, the consistency of egg white. This is the best sign of when ovulation is actually happening. It’s prime time for action.

Use an ovulation predictor kit. You can start testing with your ovulation predictor kit a few days before your estimated day of ovulation. Subtract 17 days from your average cycle length and start testing from this day of your cycle, e.g. if you have a 28 day cycle, you would start testing from day 11. A positive result means you are going to ovulate within the next 24 to 36 hours.

Record your basal body temperature (BBT) each day before getting out of bed. A special basal body temperature thermometer will ensure accurate measurement. Your BBT rises about half a degree Celsius after ovulation has occurred. By charting your temperature, it’s easy to see when the rise in temperature and ovulation happens. This can help you work out your own pattern of ovulation. However, because at that stage ovulation has already passed, it does not help you pinpoint the fertile window but may guide you for next month.

Use the ovulation calculator on this site. If you know the date of your last period, the length of your cycle and your cycle is regular, this will identify your ‘fertile window’ and predicted ovulation date.