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What Is Ovulation & When Does Ovulation Occur

What Is Ovulation & When Does Ovulation Occur

Ovulation is a phase in the menstrual cycle where the ovary releases a mature egg. In an average and perfectly regular 28-day cycle, the ovulation window is predicted to fall around day 14 of the menstrual cycle.

This article will help answer what ovulation is when ovulation occurs, how long ovulation lasts, and the female reproductive organ during ovulation.

What is ovulation


Female Reproductive Organ During Ovulation?

Image courtesy of The Bright Girl Guide by Demi Spaccavento. Female reproductive system during ovulation
    • Each female has a pair of ovaries that carry out two vital functions in a woman’s reproductive health; they release oocytes (eggs) for fertilization and reproductive hormones, mainly oestrogen and progesterone, both important in the menstrual cycle. The ovary also acts as a reservoir to the ovarian reserve of a female, which is the total amount of eggs that she would have throughout her lifetime. These premature ova or eggs are produced during a female’s fetal period and are estimated to be numbered around 2 million at birth and reduced to 400 000 eggs at puberty. In the time frame between puberty and menopause, only about 400 to 500 eggs will be matured enough and can be fertilised.
    • Ovarian Follicle/Corpus Luteum Ovarian follicles are structures within the ovaries that are physically fluid-filled sacs that house the eggs or ova. They transform the menstrual cycles where they accommodate the growth of eggs at the beginning of the cycle then regress into hormone-producing corpus luteum to sustain pregnancy should it occur at the later part of the uterine cycle.
    • Fallopian Tubes These structures act as conduits between the ovaries and the uterus, which transport the eggs or ova from the ovary via hairlike projections called cilia. If fertilization occurs, they transport the fertilized egg to the uterus for implantation.
    • The uterus is also known as the womb, is where implantation of a fertilized egg occurs and later continues to sustain a fetus throughout pregnancy. A fertilized egg will implant itself in the innermost part of the uterus, called the endometrium.
    • The cervix produces cervical mucus, which changes in consistency throughout the menstrual cycle and directly affects women’s fertility. At the peak of the fertility window, the cervix produces clear mucus, which can be referred to as egg white cervical mucus (EWCM) which aims to assist sperms with motility and increases the possibility of sperm fertilizing an egg in the fallopian tube.

What Hormonal Changes Occur During Ovulation?

The menstrual cycle and the changes occurring throughout the cycle can be broken down into 3 phases:

    • Follicular ( before the release of an egg) during the first phase of the menstrual cycle, known as the follicular phase, the body secretes follicle-stimulating hormone (FSH) to induce the growth of approximately 15-20 eggs in the ovaries, along with luteinizing hormone (LH). As the follicles grow, estrogen levels increase significantly and like a switch, this rise of estrogen inhibits FSH allowing smaller follicles to deplete in growth.
    • Ovulatory (release of an egg) the continuous surge of estrogen excites a sudden spike of LH, resulting in the final maturation of a dominant egg and extrusion from the follicle that houses it. This release of a mature egg is called ovulation and takes place 28 to 36 hours after the onset of LH surge and 10 to 12 hours after the peak of LH surge.
    • Luteal (after the release of an egg), the cells that remained in the collapsed ovarian follicle undergo a transformation and become corpus luteum which manufacture mainly progesterone that is vital to prepare the womb for implantation should fertilization occurs. This phase is called the luteal phase. If fertilization does not take place, the corpus luteum regresses, and the lining of the endometrium sheds correlating to menstruation.

The graph below summarizes the pattern of hormonal changes during each phase:

Ovulating Regularly With PCOS
Image courtesy of The Bright Girl Guide by Demi Spaccavento.


What Is A Fertile Window?

The fertile window is defined as 5 days leading up to ovulation, in addition to the day of ovulation in the women’s cycle itself. This takes into account the lifespan of both sperm, which is up to 5 days, and the egg, which is 24 hours. The Fertility Society of Australia outlined that the probability of pregnancy within these 6 days (fertile window) increases significantly and reaches 27%-33% within 3 days before and including the day of ovulation itself.

What Are The Signs Of Ovulation?

According to American Pregnancy Association, there are 3 parameters that women can effectively track at home to predict ovulation. These signs are listed as followed :

1. Change In Cervical Fluid

At the peak of the fertility window, the consistency of cervical mucus will resemble the white of an egg. This fertile cervical mucus is called an “egg white cervical mucus”. It serves as an ideal environment for sperms to swim up the vaginal canal to the fallopian tubes, where fertilization occurs. Keeping track of the consistency of cervical mucus is also part of the fertility awareness methods, which is an inexpensive way to track fertility by monitoring cervical mucus.


Vaginal discharge colours: what do they mean?
Image courtesy of The Bright Girl Guide by Demi Spaccavento.


2. Basal Body Temperature Monitoring

Basal body temperature (BBT) is the temperature when your body is at rest. Throughout the menstrual cycle, the BBT fluctuates consistent with hormonal changes but most markedly, most women experience a slight rise in BBT during ovulation. The typical BBT for most women before ovulation is 35.56 -36.67 degrees and may go up to 37.22 degrees during ovulation. When using this method to track ovulation, women are advised to take their BBT with a basal ovulation thermometer every morning at around the same time and chart the result so a pattern could be observed.

3. Change In Cervical Position Or Firmness

Checking the position and firmness of the cervix at around the same time every day could provide a clue as to whether a woman is ovulating. On fertile days, the cervical opening or os is slightly dilated, allowing for sperm to enter, softer inconsistency, and higher position than the menstrual cycle.

What Are The Secondary Symptoms Of Ovulation?

Most secondary symptoms of ovulation are highly variable and inconsistent from each woman and each ovulation window. However, if used in conjunction with other ovulation predictor signs, these symptoms can serve as helpful reminders that you are ovulating. Secondary symptoms of ovulation include:

1. Increased sensitivity to smell

An article published by Scientific American included studies that were done highlighting the sharpened sense of smell during the time frame leading to ovulation. It was postulated that women developed olfactory sensitivities to detect physical stimuli in potential partners that could suggest an ideal reproductive period.

2. Light spotting

Spotting that occurs around the time of ovulation is called ovulation spotting and is generally caused by sudden changes in hormones. In the days leading up to ovulation, estrogen levels rise steadily but are followed by a sudden drop after ovulation occurs in conjunction with a rise in progesterone. This shift in hormonal balance caused the resultant spotting experienced by women during ovulation.

3. Breast tenderness

Breast tenderness associated with the menstrual cycle is referred to as cyclical breast pain and is a common pre-menstrual discomfort. It is hypothesized that fluctuations in hormones may contribute to this symptom, particularly progesterone, which signals the breasts to retain more fluid, causing pressure to increase and the breasts to stretch slightly.

4. Cramping or slight pain on one or both side of the pelvis (mittelschmerz)

Typically, the mild cramping sensation can be experienced in the lower abdominal region on the side of the ovary, which releases the egg during the cycle. Several factors are associated with this pain, including the expansion of the ovarian follicle in the ovary and inflammation of the abdominal and pelvic lining that accompanies ovulation.

5. Increased sexual libido

During ovulation, an increase in sexual libido is nature’s way of saying, “My body is ready for a baby!”. According to research, the increased sex drive correlates with a surge in luteinizing hormone production.

6. Abdominal bloating

Abdominal bloating has been attributed to the luteal phase, where estrogen shows a dive at the beginning of the phase and experienced a sudden surge midway. This sudden surge of estrogen has been linked to an increased retaining of fluid in women, thus causes bloating.

What Are At-Home Test Available To Predict Ovulation?

An ovulation kit, also widely known as an ovulation predictor kit (OPK), has revolutionalised fertility awareness among women trying to increase their success rate of achieving pregnancy. This convenient test work based on detecting specific hormonal changes in the urine, specifically a spike in luteinizing hormone that happens approximately 12 -36 hours before the release of an egg in a female’s body. To put it simply, it assists with the detection of fertility window with a higher degree of accuracy and thus improving the probability of a successful pregnancy.

How accurate are ovulation tests?

Compared to other modes to monitor ovulation, OPKs offer higher precision and more than 99 per cent accuracy at detecting LH surge, which corresponds to ovulation. To increase ovulation prediction’s effectiveness, a woman can subsequently monitor their BBT, cervical mucus, position, and firmness to boost confidence on the best time to conceive.