Why and how to calculate your ovulation?

The female menstrual cycle unfolds in two parts, before and after ovulation:

Before ovulation comes the follicular phase

The brain produces FSH, which stimulates oestrogen production by the ovaries. Oestrogen causes follicles to mature and the endometrium to grow. Around the middle of the cycle, as oestrogen accumulates, it stimulates the production of "sperm-friendly" cervical mucus (vaginal discharge) necessary for fertility, and the brain ultimately produces LH, which triggers ovulation: an egg is released from one of the two ovaries.

After ovulation comes the luteal phase

The egg cell matures into an egg, which then transforms into the corpus luteum, producing progesterone. If fertilised, progesterone supports the implantation of the embryo in the uterine lining to begin the pregnancy, and inhibits the production of cervical mucus. Progesterone will remain elevated until birth. If there is no fertilisation, the egg will disappear, progesterone will drop, and this will trigger menstruation.

Ovulation is absolutely essential for fertility, since without ovulation there is no fertilisation and therefore pregnancy is not possible. Moreover, if ovulation is not of sufficient quality, progesterone production during the luteal phase may be inadequate to support implantation and the start of a pregnancy, which can result in miscarriage.

But ovulation is also a central event for those who do not wish to become pregnant (just yet, or ever), because it is through ovulation that sex hormones are produced — which, beyond conception, matter in many other ways.

The importance of progesterone

For example, sufficient progesterone production can help avoid the discomforts of premenstrual syndrome and thereby support quality of life, but also contributes to reducing inflammation and to supporting the production of calming neurotransmitters with anti-anxiety effects… yet without ovulation, there is no progesterone. 

The importance of oestrogen

Oestrogen, for its part, is important for bone health, memory, libido, attractiveness, energy, skin… and ovulation involves oestrogen secretion beforehand.

The menstrual cycle would thus serve very little purpose without ovulation, which drives and determines our hormonal fluctuations.

In theory, ovulation occurs in the middle of the cycle. In people with a 28-day cycle, ovulation generally takes place on day 14 (the first day of the cycle corresponds to the first day of the period).

However, many women do not have 28-day cycles or do not have regular cycles. As a general rule, each woman tends to have a luteal phase that lasts approximately the same number of days (typically 10 to 14 days), and it is the length of the follicular phase that tends to vary. On average, therefore, ovulation occurs 10 to 14 days before the period.

Identifying the day of ovulation makes it possible to:

Calculating your ovulation to optimise conception

A woman is fertile for only a few days per menstrual cycle, and this window falls a few days before and during ovulation. From the day after ovulation (the egg only lives for 4 to 24 hours), it is too late and you are no longer fertile. It can therefore be helpful for a couple wishing to conceive to know when the woman will ovulate, so as to favour unprotected intercourse before and during ovulation (sperm can survive for 5 to 7 days in the uterus) in order to maximise their chances of achieving a positive pregnancy test.

Calculating your ovulation to avoid getting pregnant

Knowing when you are ovulating and consequently when you are fertile can, conversely, help you know when it is preferable to use protection during intercourse or to abstain, in order to achieve a negative pregnancy test. This type of natural contraception requires a little practice before you can rely on it. 

Calculating your ovulation to understand your body

Ovulation signals the end of the oestrogen-dominant phase and the beginning of the progesterone-dominant phase. These hormonal fluctuations are accompanied by shifts in energy levels, and it can be illuminating to know where you are in your cycle in order to understand your moods, desires, and current state of mind. If having a baby is not on the immediate agenda, it can also be worthwhile to familiarise yourself with your body and your fertile window so as to put all the odds in your favour when the time comes.

Identifying ovulation is not always straightforward — it doesn't necessarily follow a regular schedule. Several methods can help us:

Calculating ovulation by counting backwards

The luteal phase lasts 10 to 14 days; if you have regular cycles, you can estimate that ovulation occurs 10 to 14 days before the start of your next period. If you have a 28-day cycle, ovulation therefore occurs in principle on day 14 to 18 from the first day of the cycle. This remains a tool for making an estimate rather than a fixed schedule. Some people may have a short luteal phase (shorter than 10-14 days), often due to a progesterone deficiency. In that case, counting backwards is misleading and cannot be used.

For example, the following timeline can be estimated for these cases:

If I have a typical cycle

For a cycle of 28 days, ovulation occurs in principle on day 14 to 18 from the 1st day of your period (28-14; 28-10); for a cycle of 29 days, ovulation occurs in principle on day 15 to 19 (29-14; 29-10), and so on.

If I have a short cycle

For a cycle of 21 days, ovulation occurs in principle on day 7 to 11 (21-14; 21-10);

If I have a long cycle

For a cycle of 40 days, ovulation occurs in principle on day 26 to 30 (40-14; 40-10);

If I have an irregular cycle

If it is irregular, it will be impossible to estimate the date of ovulation using this method, as you cannot know the date of your next period.

Relying on ovulation pain to calculate your ovulation window

Some of us experience what is known as mittelschmerz, a German word meaning "middle pain". This is a pain that can occur at the time of ovulation, usually in the lower left or right abdomen in a relatively localised area (at the level of the ovary that is ovulating that month).

The mechanisms behind this pain are not yet fully understood, but it appears that the ovulatory process is accompanied by inflammation, and that rupturing the wall of an ovary to release the egg can be painful for some women. It is never pleasant to be in pain, but if we look on the bright side, it can help us identify the date of ovulation.

There are other ovulation symptoms that can be observed: breast pain, back pain, abdominal pain, intense fatigue, headaches, etc. Other signs, such as an increase in libido, may also be observed.

Using an ovulation test

Like pregnancy tests, ovulation tests consist of sticks that you urinate on. If the stick detects the presence of LH (which triggers ovulation within 10 to 12 hours of its peak), the ovulation test will be positive. Otherwise it will be negative.

Using symptothermal method to calculate your ovulation window

This is a method of observing three signals from our body that indicate whether we are in our fertile window or not:

"Sperm-friendly" cervical mucus (vaginal discharge) is secreted a few days before ovulation and during ovulation under the influence of oestrogen. It allows sperm to survive in the female reproductive system in order to wait for ovulation and fertilise at the right moment. It is generally quite abundant, sticky, whitish or transparent. The cervical mucus after fertilisation has a particular appearance. During the luteal phase, progesterone inhibits "sperm-friendly" cervical mucus and therefore prevents sperm survival.

Basal body temperature

After ovulation, progesterone "warms" the body by a few tenths of a degree. The rise in temperature therefore indicates that ovulation has taken place and that it is too late to conceive. Taking your temperature is a method that must be carried out with a thermometer designed for this purpose, in the morning upon waking before getting out of bed and becoming active, and always at the same time. Please note: temperature can vary depending on many factors: infection, jet lag, too few hours of sleep, alcohol consumption the night before…

The position of the cervix

Under the effect of oestrogen, at the same time as the secretion of "sperm-friendly" cervical mucus and up to and including ovulation, the cervix opens, becomes softer and sits higher in the vagina, allowing sperm to pass through. After ovulation, under the effect of progesterone, the cervix becomes firmer, closes and sits lower in the vagina, preventing sperm from passing through.

Cross-referencing these three parameters is the most reliable way to know where you are in your cycle, but simply observing cervical mucus can already be enough. Just be aware that as we age, we produce less of it.

The symptothermal method requires practice, particularly for those with irregular or long cycles, and especially for those with PCOS.

Using an app to calculate your ovulation window

Many apps today offer a menstrual cycle tracking tool. Those that do not allow you to add information about cervical mucus, temperature and cervical position are not reliable tools, as their algorithm simply estimates the date of ovulation based on your previous cycles and its programming. Several studies highlight the fact that most apps are not based on scientific evidence, and that relying solely on an app without adequate training may not be sufficient. Nevertheless, some apps are considered accurate enough to be deemed reliable by the FDA in the United States, for example.

Identifying the date of ovulation — beyond the goal of achieving pregnancy or using contraception — is a way of reconnecting with our bodies and learning to work with our menstrual cycle, which involves so much more for us than just the period itself each month.

Do not hesitate to reach out to your gynaecologist if needed.