Updated on May 18, 2022

An explanation of the basics of ovulation

Appropriate ovulation day
hormone
Basal body temperature

Reading time: 7 minutes

Essential Knowledge about Ovulation Day 1. Explanation of the Basics of Ovulation Day

What is ovulation?
About the timing of ovulation
The mechanism of ovulation
Relationship with pregnancy

Dr. Masayuki Kinutani, Director of Kinutani Obstetrics and Gynecology Clinic

Supervision

Director, Kinutani Obstetrics and Gynecology Clinic (Medical Corporation): Mr. Masayuki Kinutani

After graduating from Ehime University School of Medicine, she worked at the Department of Obstetrics and Gynecology at Hiroshima University School of Medicine and the Sanno Hospital Reproduction Center, before studying advanced reproductive technology in Canada, the United States, and the United Kingdom. In 2002, she became the director of Kinutani Obstetrics and Gynecology Clinic. She is a certified obstetrician and gynecologist by the Japan Society of Obstetrics and Gynecology and a certified reproductive medicine specialist by the Japan Society for Reproductive Medicine.

<Things you should know> The correct knowledge about "ovulation day"
1. Explanation of the basics of ovulation

A woman's body is equipped with essential functions for pregnancy and childbirth. For women hoping to conceive, ovulation is a particularly important day. While we may think we understand the mechanism and timing of ovulation, many people don't fully grasp it. Therefore, this article will explain the relationship between ovulation and pregnancy in detail.

What is ovulation?

Ovulation is a very important day for those hoping to conceive. First, let's explain what ovulation means and its relationship to menstruation.

Glossary

Ovulation occurs when a large amount of luteinizing hormone, a hormone that signals the brain to ovulate, is secreted into a follicle in the ovary that has grown to about 18-20 mm in size. Within about 40 hours, the wall of the follicle ruptures, and the egg is released into the abdominal cavity. The day on which this ovulation occurs is called the ovulation day. Incidentally, the diameter of the egg at this time is about 0.1 mm, and it is only small enough to be seen as a white dot with the naked eye.

Relationship with menstruation

Women ovulate once between menstrual cycles. While there are individual differences, the average cycle is 25 to 38 days, and ovulation occurs around the middle of this cycle. If pregnancy does not occur, the corpus luteum begins to degenerate about 10 days after ovulation, the hormones that have maintained the uterine lining decrease, and the lining sheds about two weeks after ovulation, resulting in menstruation.

About the timing of ovulation

To determine your ovulation day, first measure your basal body temperature to understand your body's rhythm. Use a basal body thermometer and measure your temperature while still in bed as soon as you wake up in the morning. Measuring at the same time each day is best, but don't be too anxious about it; just aim to measure before getting out of bed to start with. It's important not to stress yourself out by worrying too much. By creating a chart of your basal body temperature, you can get a general idea of your menstrual cycle, whether or not you're ovulating, and your hormone levels.

While there are individual differences, typically the first two weeks of menstruation are a low-temperature phase, followed by a sharp drop at the end of that period before transitioning to a high-temperature phase, which lasts for about two weeks. If pregnancy occurs, the high-temperature phase continues, but if pregnancy does not occur, the temperature begins to drop, and menstruation occurs, shedding the unnecessary uterine lining. This marks a reset, and preparation for the next pregnancy begins again.

It was once thought that ovulation occurred on the day the blood pressure dropped sharply, but it has become clear that this is not always the case. It is more accurate to assume that ovulation occurs during the 2-3 days following the sharp drop in blood pressure.

Ideal basal body temperature

Ideally, a basal body temperature chart should clearly show two distinct phases: a low-temperature phase and a high-temperature phase. If only a low-temperature phase is observed and no high-temperature phase is seen, anovulatory cycles are suspected, and if the high-temperature phase is short (less than 10 days), luteal phase defect is diagnosed. However, some people do not ovulate even if their temperature chart shows a clear two-phase pattern, so this should be considered a general guideline.

Once you have a general understanding of your body's rhythm using a basal body temperature chart, try to predict your ovulation day. With basal body temperature alone, you'll usually only know when ovulation occurred after the fact. It's recommended to observe your cervical mucus, which is a clear discharge. The amount and concentration of cervical mucus change cyclically due to the action of estrogen. As ovulation approaches, you will start to produce a large amount of sticky discharge, similar to the white of a raw egg. If you take some on your finger, it will stretch for more than 10 cm, which is a sign that ovulation is imminent. This condition continues for more than 3 days, and ovulation occurs about 2 days after the discharge, when the amount is at its highest. The amount of discharge often decreases on the day of ovulation.

By using a basal body temperature chart and cervical mucus analysis together, it becomes easier to predict ovulation. Furthermore, using ovulation prediction test kits, which can be purchased at pharmacies and other stores, allows you to predict ovulation about one day in advance, making it even easier.

The mechanism of ovulation

Approximately once a month, one egg is released from the ovary during ovulation. During menstruation, the hypothalamus in the brain sends a signal to the pituitary gland, which secretes follicle-stimulating hormone (FSH) to encourage the formation of mature follicles. The stimulated follicles develop and eventually secrete estrogen, a type of follicular hormone. This hormone causes the uterine lining to thicken.

When a follicle matures and produces enough estrogen, the pituitary gland releases luteinizing hormone, signaling the body to ovulate. The follicle's membrane then ruptures, releasing the egg from the ovary, resulting in ovulation.

The released egg is taken up by the fallopian tube, and if it encounters sperm, it is fertilized. The resulting embryo is then sent to the uterus, where the uterine lining has thickened, and implants. If the egg does not encounter sperm, the uterine lining, which had thickened to facilitate implantation of the embryo, sheds, and menstruation begins.

Even if a woman ovulates for 30 to 40 years, she will only ovulate a few hundred eggs in her lifetime. The vast majority of the remaining eggs will not be ovulated and will simply disappear.
Around the age of 50, the eggs prepared for ovulation become depleted, and ovulation and menstruation stop. This is menopause.

Menstruation and the Mechanism of Hormones

The hypothalamus is responsible for issuing signals for hormone production. In essence, the hypothalamus is the control center for hormones. Since the hypothalamus also contains the center of the autonomic nervous system, a disruption in the control of the autonomic nervous system can affect the hypothalamus, leading to hormonal imbalances. This is why stress on the mind and body can easily disrupt the menstrual cycle.

Relationship with pregnancy

After ovulation, the egg is released from the ovary and taken in by the fimbriae, which resemble sea anemones at the end of the fallopian tube, where it waits for sperm to arrive in the ampulla of the fallopian tube. Sperm that have overcome numerous challenges meet the egg and fertilization occurs. The fertilized egg then undergoes repeated cell division and implants in the uterine lining 6 to 7 days after fertilization, leading to pregnancy.

When trying to conceive, many people get excited once they can predict their ovulation date. However, ovulation is not the only day when conception is possible.

In fact, sperm can survive in a woman's body for about 2-3 days. On the other hand, an egg can only be fertilized for about 12-24 hours. Therefore, if timed correctly, there is a possibility of pregnancy even 4-5 days before ovulation. Also, cervical mucus peaks 2-3 days before ovulation, so the time with the highest chance of conception is said to be "2 days before ovulation," when the cervical mucus is thinner and sperm survival rates are higher. From this, it can be said that the period from 3 days before ovulation to about 5 days after ovulation is the most fertile time.

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