The ovarian cycle: Ovulation and tracking, hormones, fertility, pain and other symptoms

Key takeaways:

• Ovulation occurs when the ovary releases a mature egg, which travels to the fallopian tubes, where a sperm fertilizes it (if present). 
• The ovarian cycle consists of three phases, which include: the follicular phase, the ovulatory phase, and the luteal phase. Different reproductive hormones, such as progesterone, estrogen, and luteinizing hormone, control these phases. 
• Methods such as monitoring changes in cervical mucus, tracking basal body temperature, and using ovulation predictor kits are ways to track the ovarian cycle and can help increase the chances of getting pregnant.

Ovulation means the release of a mature egg (also called an ovum) from the ovary, which happens once in an ovarian cycle. The released egg travels to the fallopian tube, where it waits to be fertilized by sperm, if present in the uterus. 

The ovarian cycle takes place simultaneously with the menstrual cycle, meaning the two cycles are intertwined.

The ovarian cycle consists of three phases, with ovulation happening approximately halfway through the cycle.

Ovulation usually takes place around day 14 in a 28-day cycle (i.e., counting from the first day of menstruation). However, for women with shorter or longer cycles, the timing of ovulation may vary.

The released egg can survive for less than 24 hours after ovulation. During this time, it can be fertilized by sperm, after which the fertilized ovum implants into the wall of the uterus, and the pregnancy journey continues.

But if fertilization does not occur, the body will absorb it, and the inner part of the uterus (endometrium), which thickens in preparation for pregnancy, begins to shed. This shedding will now result in menstruation and mark the beginning of a new cycle.

This article aims to explain what ovulation is, the ovarian cycle, the hormones that are involved in the ovarian cycle, and how to track ovulation.

What is the ovarian cycle?

The ovarian cycle is the whole process it takes for one of the ovaries to release a mature egg every month, starting from the development of eggs in the primordial follicles. 

The cycle starts from the first day of menstruation and ends right before menstruation. It also lasts an average of 28 days, and the first time most females have their ovarian cycle is during puberty.

Phases of the ovarian cycle

The ovarian cycle has three phases, which are:

1. Follicular phase

Female reproductive eggs form during fetal development (when a baby is still forming in the womb) and are contained within primordial follicles in the ovaries. These follicles are like the starting point of a woman's reproductive process. 

At birth, females already have millions of eggs in their primordial follicles, and that’s all the eggs they can ever have, as they are unable to make new eggs after birth. However, most of these primordial follicles go into a kind of sleep mode and don't develop until puberty.

Each month, around 20 of these follicles start to grow, but only one becomes a secondary follicle, which is bigger in size. A few days before ovulation, the secondary follicle becomes a dominant follicle, which releases the egg. 

The follicular phase starts on the first day of menstruation and lasts for about 12–16 days (depending on the length of a person’s cycle), ending when you ovulate.

2. Ovulatory phase

The ovulatory phase starts when an egg is released from the ovary. It is the shortest of all the phases, lasting for less than 24 hours.

Ovulation is triggered by a rise in luteinizing hormone (LH). This surge in LH is initiated by a significant increase in the estradiol hormone secreted by the dominant follicle. The released egg then travels down the uterine tube in readiness for fertilization.

3. Luteal phase

The luteal phase comes after the ovulatory phase. After ovulation, the remains of the mature follicle from which the egg was released form the corpus luteum.

The corpus luteum produces hormones like progesterone and estrogen, which prepare the uterus for pregnancy. If fertilization doesn't occur, these hormone levels drop, the corpus luteum dies off, and another menstrual cycle begins.

However, if pregnancy happens, the corpus luteum produces more progesterone to preserve the pregnancy until the placenta can produce enough hormones to support it.

The time from the release of an egg to the start of a period is also around 10 to 16 days.

Hormones that play a role in the ovarian cycle

Several hormones play important roles in the ovarian cycle. These hormones include [6]

Follicle-stimulating hormone (FSH)

During the follicular phase of the ovarian cycle, FSH is released by the pituitary gland to help the ovarian follicles that contain the eggs mature. As the follicles grow, one of the follicles becomes dominant and starts releasing hormones called estradiol and inhibin.

Estradiol (estrogen)

Estradiol is a type of estrogen hormone produced by the dominant follicle as the follicle grows. As the follicle produces enough estradiol, it reaches a level of around 200 to 300 pg/ml and maintains it for about 48 hours.

Estradiol also works by suppressing the release of FSH to prevent the development of other follicles.

Inhibin hormone

Inhibin is another hormone secreted by the dominant follicle. As inhibin levels rise, it further suppresses FSH secretion, allowing the dominant follicle to continue developing.

Gonadotropin-releasing hormone (GnRH)

GnRH is produced by the hypothalamus, a part of the brain. This hormone stimulates the release of gonadotropic hormones from the pituitary gland.

During an ovarian cycle, GnRH levels increase when the dominant follicle produces enough estradiol. This increase triggers the release of LH and FSH.

Luteinizing hormone (LH)

LH is released by the brain in response to the surge of GnRH. A surge in LH is what triggers ovulation, which is the release of a mature egg from the dominant follicle. LH also stimulates the transformation of the empty follicle into the corpus luteum.

Progesterone

Progesterone is produced by the corpus luteum, which is formed from the remnants of the follicle after ovulation. Progesterone thickens the inner lining of the womb, enhances blood flow, and supports the maintenance of pregnancy if fertilization occurs.

If pregnancy doesn't happen, the corpus luteum breaks down, causing progesterone (along with estradiol) levels to drop, leading to the start of a new cycle.

Ovulation, conception, and pregnancy

During ovulation, an egg is released from the ovaries, which then travels through the fallopian tubes. If you have unprotected sex around this time, the egg is most likely to meet sperm in the fallopian tube and get fertilized. 

When someone does not ovulate, it means that their ovaries did not release a mature egg that month. This condition is called anovulation. Without ovulation, there is no egg available for fertilization, making it impossible to conceive naturally.

There can be various causes of anovulation. Some of these include:

• Stress
• Radiation therapy
• Chemotherapy medication
• Excessive weight loss or weight gain
• Women with premenopausal syndrome
• Teenagers who just started menstruating
• Ovarian dysfunction, such as presence of ovarian cysts in the ovaries
• Hormonal imbalances such as Polycystic ovary syndrome (PCOS)

Symptoms: How to tell when you are ovulating

Listed below are the most common symptoms of ovulation. However, these can vary from person to person. It is also normal to notice some of them one month and not notice them in the next.

• Breast pain
• Abdominal bloating
• Increased urge to have sex
• An increase in body temperature
• Changes in cervical position
• Ovulation pain (mittelschmerz)
• Clearer and more slippery cervical mucus

Ways to track ovulation

Below are some methods you can use to track ovulation:

1. Changes in cervical mucus

Around the time of ovulation, the cervical mucus in some women tends to become clear, slippery, and stretchy, resembling the consistency of raw egg whites. Cervical mucus is the fluid or gel-like discharge secreted by glands in the cervix and is known to facilitate sperm movement.

2. Basal body temperature (BBT) changes

A slight increase above 1 degree Fahrenheit may indicate an ovulation. This temperature reading can be done at home using a thermometer. 

3. Ovulation pain

Ovulation pain is also known as mittelschmerz. Some women experience mild abdominal pain on one side of their lower abdomen around the time of ovulation. This can be a sign that an egg has been released.

4. Changes in cervical position

During ovulation, the cervix may become softer, higher, and more open in some people. If you have been regularly checking the position of your cervix, you may be able to detect changes that indicate ovulation.

5. Ovulation predictor kits (OPKs)

OPKs are urine-based tests that detect the surge of luteinizing hormone (LH) that occurs just before ovulation. These kits can help predict when ovulation is about to occur and can be useful for women who are trying to conceive.

Conclusion

Ovulation is a critical process in the ovarian cycle and is essential for fertility. The ovarian cycle is regulated by hormones such as FSH, estrogen, LH, and progesterone and consists of three phases: the follicular phase, the ovulatory phase, and the luteal phase. 

If you are trying to conceive or want to track your ovulation, it may be helpful to use a combination of the methods listed in this article and consult with a gynecologist for more professional guidance, if needed.