Fecundation: everything you should know

Fecundation is the process by which the female reproductive cell, the ovule, and the male, the sperm, merge to create a new, unique and irreplaceable being.

Human fertilization is a complex process in which many elements and factors come into play. It is the fusion of an egg and a sperm to create a new being , unique and different from all those that exist. From this union arises the embryo and, if it is implanted correctly, pregnancy will occur.

How fertilization occurs

In humans, this process is internal. That is, it takes place inside the body of the woman, specifically in the fallopian tubes. This is the so-called natural or in vivo fertilization .

However, this type of fertilization is not always possible. For this reason, assisted reproduction has been developed , in which fertilization takes place in a laboratory . It is also known as artificial fertilization or in vitro fertilization .

Next we will develop the stages of this complex process. From the separate existence of the gametes (sex cells) to their union and the implantation of the embryo we can distinguish four phases.

1.The sperm go to the ovule

"Out of hundreds of millions of sperm, only one will manage to enter the ovule and fertilize it"

During intercourse, sperm penetrate the vagina. This is an acid medium harmful to them, so they migrate. Through the cervix , they reach the uterus and from there to the fallopian tubes , where the egg will be found.

In the tubes, the sperm can survive between 48 and 72 hours. On the contrary, outside of the feminine body its life is reduced to less than 24 hours. This means that fertilization can occur even two or three days after the sexual encounter.



Semen contains hundreds of millions of sperm. However, barely a hundred of them will manage to reach the ovule; the rest is exhausted and dies. And among these "survivors", only one will get into the female gamete and fertilize it .

2. Union of the ovule and sperm

Upon entering the ovule, the sperm loses the tail and fuses its nucleus with that of the female cell . From this union is born the first cell of the embryo: the fertilized egg or zygote . Here all its unique genetic information is already contained: from its sex to the color of eyes or hair.

Regarding the ovule, when fertilization occurs, it alters its chemical structure. The membrane that surrounds it, until then permeable, now closes the passage to the rest of spermatozoa. If more than one male gamete entered, fertilization would be unfeasible .

3. Travel from the zygote to the uterus

In the fallopian tubes there is a kind of hair called vibrating cilia. Thanks to the movement of these and the muscular impulses of the tube the fertilized egg moves. The displacement to the uterus will last about three or four days .

During this trip, the zygote will begin its development and evolution . A few hours after fertilization, it will be divided into two cells and will continue to unfold in equal parts. When it reaches the uterine cavity, it already consists of 16 cells.

However, when it reaches the uterus it does not nest immediately, since it has not yet reached the necessary development . Will remain free two or three days, suffering new modifications before implanting in the uterine mucosa.

4. Implementation

"Only 30% of embryos successfully implanted in the womb"

The implantation takes place 7 days after fertilization . Normally, it will occur around 21 or 22 days after the start of the last rule. The zygote is placed on the endometrium and adheres strongly, like a suction cup.

The outer layer of the egg creates a kind of nest and forms the trophoblast , a membrane that will then give rise to the placenta . This will nourish and protect the baby during pregnancy. From this moment, the development of the embryo is constant.

The fertilization of twins

Contrary to what popular beliefs indicate, twins do not arise from the fertilization of an egg by two sperm. The mechanisms of fertilization prevent this, since the resulting embryo would be unfeasible.

So that twins can originate , the process is identical to the one that gives rise to a single embryo. However, sometimes and for reasons still unknown, the embryo is divided into two, giving rise to two genetically identical babies. This implies that they will also be, obligatorily, of the same sex.

On the other hand, the origin of the twins is different. In this case , the fertilization of two different ovules occurs, each one by a spermatozoon. Therefore, the development of embryos would be the usual. The twins will not be genetically identical nor do they have to be of the same sex.