What happens when an egg is fertilized

Fertilization: This is how your pregnancy begins

Fertilization can take place within a few hours after ovulation. We have put together the most important information about your ovulation here. The cycle of life begins with the fertilization of a mature egg. From a purely medical point of view, pregnancy begins on the first day of your last period. But since nobody can say exactly when your ovulation will take place and when the mature egg will then be fertilized, it is recognized that pregnancy can be expected from the last menstrual period. But what exactly happens in your body after a mature egg cell meets the male sperm?

Fertilization only possible for a few hours

The mature egg is ready for fertilization just a few hours after ovulation. This means that it is best to have intercourse about two to three days before you ovulate. But you should know that the probability of getting pregnant is often only around 15-25 percent. And only one in a million sperm makes its way into the egg cell! Many of them lose the race “within the first few meters” because only a few hundred sperm get to the fallopian tube. To do this, they first have to go through the uterine mucus, which develops ’" sperm-friendly "during the cycle. This means that this mucus is usually impermeable to sperm. But the closer you get to your fertile days, the more permeable this mucus becomes - and the higher the chance that the sperm will get through. If the mucus is permeable to sperm, they “wait” in the uterus for a few days after ejaculation. There is a friendly atmosphere here. Therefore, they can survive for up to six days.

Sperm is getting ready for fertilization

So when ovulation occurs, the mucus plug becomes permeable and the sperm can now make their way through the cervix to the mature egg. To prevent the sperm from “getting lost” and possibly ending up in the wrong fallopian tube, the ovary, which contains the mature egg, sends a signal. Attractants - so-called chemotaxins - are sent out to prepare the way for the sperm. Every sperm has receptors on its head. These enable the attractants to be absorbed and point the sperm in the right direction.

Attracted by the attractants, each sperm tries to overcome the great hurdle in front of it. The mature egg cell is surrounded by a kind of protective cover, so-called auxiliary cells. This must first be penetrated. And that's not that easy: if fertilization is to take place, the “winning sperm” must first penetrate the plasma membrane of the mature egg cell. But that's not all: In addition to the protective cover, the egg cell is also surrounded by special glycoproteins. The sperm must also work its way through this.

But the sperm has a little help: a cap made of enzymes helps it penetrate the protective covering and the plasma membrane. Once the sperm has found its way into the interior of the cell nucleus, the outer protective layer changes immediately. The chemical composition changes and ensures that no further sperm can penetrate. And it is precisely at this point in time that the actual fertilization takes place: as soon as a sperm has penetrated the egg cell, it is considered fertilized.

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DNA already at fertilization

At the moment when the egg cell and sperm combine, i.e. fertilization takes place, the genetic information (DNA) is also transferred. Egg and sperm each contain 50 percent of hereditary information - and this creates a complete set of chromosomes. However, not both have the same “say”: Because whether the child becomes male or female, the sperm, i.e. the father, decides. All other hereditary factors such as hair color, eye color, size, etc. are decided by nature.

From now on, the fertilized egg cell also has a different name: It is now called “zygote”. For the next 30 hours or so she is at home in the fallopian tube and rests a little here. Cell division then begins. With each division, the cells are doubled, i.e. one cell becomes two, two cells become four, four cells become eight, and so on. About the fourth day after fertilization, the cell division has become a morula. And that is the signal for the egg cell to make its way to the uterus. When the egg cell gets there, a liquid comes through the membrane pores and practically floods the spaces between the cells. This leads to the fact that what is known as a blastocyst is now formed.

What else can go wrong now?

Normally, the path for the egg to the uterus (uterus) is not dangerous. However, it can happen that the mucous membrane is stuck together and the egg cell gets stuck there. In the worst case, this can lead to an ectopic pregnancy. However, this rarely happens - because after fertilization the egg cell usually arrives safely and safely in the uterus and can implant there. Once in the uterus, it first looks for the right place for the implantation. With the docking and anchoring in the uterine lining, the baby begins to develop.


Our texts on health topics are in no way a substitute for a doctor's visit.
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