How does ovulation lead to fertilization?

What is fertilization?

The fertilization of the woman's egg by the man's sperm requires, on the one hand, many framework conditions that must be met for the fertilization process, on the other hand, it is divided into several individual steps. Therefore, human reproduction is a highly complex and therefore very fault-prone process system.
Not only proper egg and sperm maturation are essential for fertilization, the time of unprotected sexual intercourse and the anatomical conditions of the female and male sexual organs also play an important role in egg fertilization.

Process of fertilization

A woman's menstrual cycle is relatively wide in time and can typically last between 25 and 35 days. In the following, the frequent 28-day cycle is assumed as an example.
In the first fourteen days of the cycle, counting from the first day of the period, what is known as follicular maturation occurs in the ovary under hormonal control. As a result, individual egg cells become larger, although usually only one dominant egg cell is actually ready to jump via a selection mechanism.
Ovulation occurs around the fourteenth day. This causes the dominant follicle to burst and the egg cell is released from the ovary into the free abdominal cavity for a brief moment. From there, the egg cell passes through the nearby fimbria funnel into the fallopian tube, the most common place of egg fertilization.

As part of sperm production, known as spermatogenesis, the man produces mature sperm in several individual steps. This process, which takes around 65 days, normally results in the formation of healthy and motile sperm.
Up to 600 million sperm get into the female body via the sperm that is released into the woman's vagina during sexual intercourse during the man’s sexual climax.
The sperm ascend through the vagina into the uterus, from where they enter the fallopian tubes. On the way to be covered, the vast majority of the sperm perish, the rest undergo another maturation process that is essential for fertilization. On the one hand, the sperm wall becomes thinner and, on the other hand, it promotes the mobility of the sperm. Both make it easier to penetrate the egg cell membrane.

The sperm then penetrates the egg cell in the fallopian tube. This process is only possible over a short period of time, because after ovulation the egg cell can be fertilized for a maximum of 24 hours.
Then the cell nuclei and thus the chromosome sets of the sperm and the egg cell fuse during what is known as conjugation. The result is the zygote, a cell capable of development and division, which now migrates into the uterus through numerous division processes in order to nestle there.

Duration from ovulation to fertilization

The time between ovulation and fertilization is very short and only a few hours. The reason for this is that the egg cell is only capable of fertilization for 12-24 hours.
Within this time window, the sperm and egg must meet and unite, as otherwise the egg perishes and dies. Fertilization is therefore only possible again in the next cycle after ovulation.

Can you feel ovulation?

Some women feel their ovulation in the form of so-called middle pain or ovulation pain. This means a slight, pulling pain in the abdomen.
Middle pain is by far not felt by all women and, if at all, then often not perceived as pain at all, but merely as a pulling feeling. This is often so weak that it is ignored in everyday life and is often not even consciously noticed.
Middle pain usually occurs in the middle of the cycle, which is why the term intermenstrual pain is also used. They occur individually either indefinitely in the abdomen, but some women can localize the feeling more precisely and assign it to the right or like side.

Read more about whether you can feel ovulation.

Can you feel the fertilization?

The egg cell's fertilization process cannot be felt. Both the egg and the male sperm are very small in size. In addition, they are not connected to the sensory system, which is why fertilization itself cannot be felt.
In the further course, however, implantation can be accompanied by noticeable symptoms. However, these do not occur regularly, which is why many women initially do not notice the implantation.
The typical physical changes are usually noticeable only when the pregnancy is developing.

How do I recognize implantation?

Several signs can point to fertilization with subsequent implantation of the embryo. It is important to emphasize that some possible signs of fertilization that have occurred are imprecise and by no means conclusive.

Unsure signs

The changes mentioned below can also be symptoms of other processes in the body or even indications of diseases.

  • One possible change can be the so-called implantation pain. About five to seven days after fertilization and the migration of the germinal system through the fallopian tubes into the uterus, women feel a slight, tugging sensation in the abdomen. However, real pain is not felt during implantation.
  • The so-called nidation bleeding can also be an indication of implantation. During the implantation process, there is a slight injury to the built up and well-perfused uterine lining. This can be felt as a small amount of bleeding from the vagina. The amount of blood excreted is usually small and roughly corresponds to the amount of bleeding on the last day of menstruation or spotting, for example when taking pills. The time of nidation bleeding can be between seven and fourteen days after ovulation and is often misinterpreted as a menstrual bleeding.

In the further course the following signs occur:

  • The most common, self-detectable sign of fertilization and thus the development of a pregnancy is the absence of the menstrual period.
  • Other, albeit uncertain and unspecific, signs of fertilization that has taken place are morning sickness and vomiting after a few weeks.
  • In addition, many women report pain, a feeling of tension and an increase in the size of their breasts shortly after the start of pregnancy and thus fertilization.

Safe signs

  • The pregnancy hormone HCG can be detected using over-the-counter pregnancy urine tests or by taking a blood sample from a doctor.
    However, a negative test does not necessarily rule out pregnancy. The concentration of the HCG at the time the test is carried out may simply still be too low to be detected.
    If you are unsure, it is advisable to avoid alcohol and nicotine as a precaution and to repeat the test in due course.
  • It is then necessary for the gynecologist to determine the position of the pregnancy using ultrasound diagnostics. If the representation of an embryonic plant in the uterus is successful, this is one of the sure signs of a successful fertilization with a proper place of implantation.
    A lack of fruiting in the uterus with a positive pregnancy test and a lack of menstrual bleeding can be an indication of an extrauterine pregnancy, for example. In the process, the egg cell is fertilized, but not physiologically migrated into the uterus. The dividing cell structure remains in the fallopian tube and can cause serious complications.
    A fruiting plant that cannot be displayed can also simply indicate a very early pregnancy with an embryo that is still too small for ultrasound diagnosis.
  • Evidence of a child's heartbeat also requires fertilization and is considered to be conclusive.

How likely is it that fertilization will occur during ovulation and sex?

The average probability of fertilization depends on the time of sexual intercourse in the fertile time window. The probability increases the closer it is to ovulation. The fertile window is usually five days before and one day after ovulation.
The average chance of fertilization is around ten percent if intercourse takes place five days before ovulation. The highest probability of around 25-30 percent can be achieved one day before and on the day of ovulation.

When is the best time to have sex so that ovulation leads to fertilization?

In order to determine the optimal time for sexual intercourse leading to fertilization, it is essential to know about your own monthly cycle. Since this can vary in length from woman to woman, it is also impossible to make a general statement as to when ovulation takes place and thus sexual intercourse is most likely to lead to fertilization.
It is therefore advisable to first carefully observe the monthly cycle, for example with the help of

  • the temperature method,
  • with the help of commercially available urine tests that can determine ovulation or
  • with the help of numerous online calculators or tables, which can be consulted as an orientation aid during a regular cycle and predict the time window possible for fertilization.

Read our articles about this:

  • Ovulation and temperature
  • What is the best way to calculate ovulation

Since the cracked egg can only be fertilized between 12 and 24 hours, sexual intercourse around ovulation is the optimal time to enable fertilization. Sperm have a maximum lifespan of around five days, which is why the five days before ovulation are included in the so-called fertile time window. In addition, there is another fertile day after ovulation, which reflects the maximum fertilization time of the egg cell of 24 hours. In total, you get six fertile days.

With a 28-day cycle, the optimal time to have sexual intercourse and get pregnant would be around day 9-15. The greatest chance of fertilization can be achieved by intercourse one to two days before and on the day of ovulation.

Find out everything about the duration of ovulation and the fertile days.

Origin and maturation of the sex cells

Maturation of the egg cell (oogenesis)

Even as an embryo, the genitals (Gonads) the woman has millions of female sex cells (Oogonia) created. A large part of the oogonia is lost by puberty, so that only 40,000 of them remain until sexual maturity for fertilization of the egg cell.
All oogonia still contain the double (diploid) set of chromosomes (46XX) and must be divided by two maturities (meiosis) are transformed into haploid germ cells (23X) so that the union of egg cell and sperm (fertilization of the egg cell) creates a diploid egg cell (46X?).

In order for ovulation to occur, the interaction of female hormones in the organism must be guaranteed.
First, the concentration of the follicle-stimulating hormone (FSH) released by the pituitary gland increases. The follicles form FSH receptors in their inner granular layer.
The more FSH receptors a follicle has, the more estrogen is produced by the follicle. The follicle with the highest estrogen production becomes dominant under the influence of FSH together with the luteinizing hormone (LH) and leads to the demise of the other follicles.
The estrogen produced by the dominant follicle has an inhibitory effect on the release of FSH, which means that other follicles are destroyed and LH ultimately takes over.
LH promotes the conversion of hormone synthesis in the granulosa cells to the production of luteal hormone (progesterone). Ovulation occurs approximately 44 hours after the LH surge begins.
The corpus luteum develops from the rest of the remaining follicle (Corpus luteum). The luteal cells of the corpus luteum develop from the granulosa cells and produce progesterone to maintain a possible pregnancy. The secretion maximum is reached on the 7th day after ovulation, the time of possible implantation of the egg. If the egg nests, the corpus luteum forms the corpus luteum graviditatis. Otherwise the corpus luteum perishes.

It must be remembered that the woman's cracked egg must be fertilized within 12 hours for implantation to take place.

Illustration of secondary follicles (A), indirect cell division (B) and internal female genital organs (C)
  1. Basin -
    Membrana basalis folliculi
  2. Granular layer
    (seed-rich layer
    of follicle cells) -
    Epithelium stratificatum
  3. Granules -
  4. Basic tissue of the ovary -
    Stroma ovarii
  5. Egg cell - Ovocytus
  6. Cell nucleus - Nucleus
  7. Glass skin - Zona pellucida
  8. Uterus - uterus
  9. Sheath - vagina
  10. Ovary - Ovary
  11. Fallopian tubes - Tuba uterina
  12. Polar bodies

You can find an overview of all Dr-Gumpert images at: medical illustrations

Sperm maturation (spermatogenesis)

The male germ cells are also subject to meiosis, so that diploid sex cells become haploid (half a set of chromosomes). In contrast to women, sperm taogenesis only takes place at the beginning of puberty and lasts for a lifetime.
Under the influence of androgens, around 1 million sperm are produced in the testes of sexually mature men every day. The primary spermatocyte with two-chromatid chromosomes and a diploid set of chromosomes develops from the spermatogonia. After the first meiosis, the primary spermatocyte gives rise to two haploid secondary spermatocytes.
After the second meiosis, two secondary spermatocytes finally develop into four haploid spermatids with a haploid chromosome set and one-chromatid chromosomes. Two spermatids each contain the X chromosome, while the other two have the Y chromosome.
The spermatids then mature into sperm (Spermatozoon) in the epididymal duct (Epididimydis duct) out.

During intercourse (Cohabitation) the spermatozoa reach the prostate gland through the epididymal duct (prostate) and together with the glandular secretions from the prostate and vesicle gland form the ejaculate for possible fertilization of the egg cell. This is expelled from the urethra towards the vaginal vault.

The ejaculate is an alkaline, fructose-rich liquid and represents the optimal environment for the motility and survival of the spermatozoon. The spermatozoon consists of the sperm head with the genetic material it contains, the movable middle part and the sperm tail.

Process of fertilization and pregnancy

The fertilization of the egg cell describes the process that occurs when a mature egg cell and a mature sperm cell (Spermatozoons) takes place. From a purely medical point of view, there is a union of two simple (haploidr) Sex cells to form a diploid egg cell (zygote) in the ampullary part of the fallopian tube (Tube) instead of.

There are three stages in the fertilization of the egg.

  • In the first stage, the spermatozoon penetrates the outermost shell (Corona radiata) of the egg cell.
  • In the second stage the inner shell (Zona pellucida) enzymatically dissolved by the acrosome.
  • In the last stage, the plasma membranes of the two sex cells fuse together.

After the egg has been fertilized, the early development phase begins after fertilization. This takes one to three weeks and involves the migration of the egg from the tube towards the uterus. Furthermore, the egg cells implant in the uterine lining (endometrium) at the beginning of neurulation.

The embryonic period begins after early development. It extends from the fourth to the eighth week of pregnancy and is important for determining the position of the organs and the basic shape of the body.

In the ninth to thirty-eighth week of pregnancy, organ growth and sexual maturation take place in the fetal period.

Conditions of fertilization

In order for the actual fertilization to take place, the man's sperm must overcome many obstacles in order to get to the fallopian tube.
Even the acidic environment in the vagina reduces the 300-500 million sperm initially present in the ejaculate to 300,000.

Only in the cervix (Zerviks) there are better conditions for the spermatozoon, because there, like in the ejaculate, an alkaline environment prevails. The longitudinal threads in the cervical mucus are beneficial for the further movement of the sperm. Sperm with malformations get caught by threads in this latticework.
Another part of the sperm is deposited in indentations (Crypts) of the cervical canal and then slowly released again later. Further sperm are sorted out in the uterine lining, so that around 500-800 sperm are left in the area of ​​the tube (fallopian tube).
As the sperm make their way through the female genital tract, they go through the final step of their maturation (Capacitation). The cleaving enzymes in the sperm head in the area of ​​the acrosome are activated in order to penetrate the egg cell from the outside.
If one of the many hundreds of sperm cells succeeds in completely penetrating the egg cell with its two shells, the way into the egg cell remains blocked for the other sperm. The cortical reaction of the egg causes the outer layer to harden and thus prevents polyspermia. Multiple sperm invasions result in non-viable egg cells.
As soon as the cell membranes of the two germ cells fuse together, the pronuclei are formed in the sperm and the egg cell (Pronucleus) with the haploid single-chromatid chromosomes.
While the secondary oocyte finishes its second maturation, the sperm transforms itself into the pronucleus by separating from the sperm tail. The coming together of both haploid nuclei is called conjugation. The nucleus resulting from the conjugation is the zygote.

Requirements for implantation

In order for the zygote to move from the tube (fallopian tube) to its place of implantation in the uterus, the tube muscles must contract in the direction of the uterus.
Furthermore, there is a flow of fluid directed towards the uterus and the ciliate stroke. In the course of its transport, the mature egg cell is subject to cell division.
Up to the eighth cell division one speaks of an omnipotent egg cell. This means that if a cell were to break away from this multicellular structure, it could become an independent organism.
The egg cell reaches the uterine lining in the state of a blastocyst. The trophoblast is on the outside and the embryoblast is in the fluid-filled space on the inside. The differentiation of the trophoblast is crucial for the uterine lining to accept the implantation of the single cells.