The differences between 'zygote', 'embryo' and 'fetus' during pregnancy

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Within the world of reproductive biology, there are words that lead to confusion in the future parents, especially in those who face fertility treatment. At this time, everything is new to them and they must face a multitude of explanations from the specialists.

This is the case of the words zygote, embryo and fetus. All refer to the future baby during the prenatal stage. However, the difference is found in the different stages of development through which the baby passes during the 9 months of pregnancy.

It is very common to confuse these 3 concepts if you do not have basic knowledge of reproduction. Therefore, it is important to know their meaning and know how to distinguish them.

Below you have an index with all the points that we will discuss in this article.

Index

The differences between 'zygote', 'embryo' and 'fetus' during pregnancy

Zygote formation

The zygote is the first stage of life and appears after the union of the ovum and the sperm, that is, after fertilization. It consists only of one cell, the first cell of the future baby, and its size is equal to that of the egg.

Fecundation refers to the fusion of male and female gametes, both with half the genetic material that the rest of the cells of an organism (46 chromosomes) due to the chromosomal reduction that they have suffered with meiosis.

The result of this fusion is the reestablishment of the normal genetic endowment of the human being, a new cell with a nucleus and 46 chromosomes, 23 of maternal origin and 23 paternal, that is denominated zygote.

Fertilization and formation of the zygote

The zygote appears on day 1 of embryonic development in the fallopian tube of the woman, which is where the fecundation takes place. From here, it begins its way to the uterus, where it will implant so that pregnancy can occur.

The zygote, which is a single cell, begins its cell division the day after fertilization. At this time, it ceases to be called a zygote and becomes an embryo on day 2 that already has about four cells.



Development of the embryo

The stage of the embryo ranges from day 1 of embryonic development, which is still called zygote, to the eighth week of gestation. During this period of time, the embryo increases in size, multiplying its cells and undergoes strong cellular changes.

The number of cells and the rate of embryonic division is called morphokinetics. Although each embryo is unique and can be divided more or less quickly, there are certain patterns of division that mark if an embryo is of good quality.

On the other hand, during the initial stages of development, the embryo can acquire other names depending on its appearance as, for example, morula or blastocyst.

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