Knowing the sex of the baby has always been one of the great unknowns of pregnancy . Many methods have been popularly used to find out the sex of the baby. Here we expose the scientific means to find out.

Formerly it was one of the most wonderful mysteries of the gestational process, since there were not enough methods to find out in advance what the sex of the new being would be. As science advanced , prenatal diagnostic techniques also advanced , offering future parents the possibility of knowing the sex of their baby.

Baby’s gender: will it be a boy or a girl?

It is not our intention to give a complete and exhaustive class in embryology (the science that is in charge of the study and development of the embryo, from its inception to the total formation of the being), but rather to offer an exhaustive exposition of those aspects that couples are really interested in and are not aware of. . It should be clear that the determination of sex in the male or female sense is acquired at the time of fertilization , depending solely on the presence of the Y chromosome in the sperm .

Every human contains 46 chromosomes in its cells. Chromosomes contain all the information of an individual in a compressed way but only 2 of the 46 chromosomes will be responsible for determining the sex of the individual. At the time of fertilization, the ovum or primordial female cell, which has a 23 X chromosomal endowment, will unite with the male sperm, which may be 23 X or 23 Y. The union of the two will give us two possibilities: a embryo 46 XX or 46 XY. If the embryo is 46 XX , it will be genetically a female individual, and if it is a 46 XY embryo , it will be a genetically male embryo.

Apart from the genetic potential of the embryo, sex will also be influenced by the hormonal environment , which will take care of the external appearance or phenotype of the fetus. As an example, we have alterations such as the Morris Syndrome with which we will have an individual with the appearance of a woman, but if we look at his chromosomes we will see with surprise that he has 46 XY, that is, genetically he is a male but he is female in appearance.

Techniques to know the sex of the baby

There are two very different ways to find out the sex: thanks to invasive techniques and thanks to non-invasive techniques.

The earliest invasive technique that we currently have is the chorionic biopsy , which consists of taking a small sample of the placenta through the neck or through the belly under ultrasound control. This technique can be performed from the 9th week of pregnancy and is intended for couples who have a high genetic risk of having an altered embryo.

Another invasive technique is amniocentesis, which is performed at 15 weeks of gestation and is the  prenatal diagnostic technique par excellence. With this technique we will have the diagnosis of sex with certainty but it is not done for this. This  invasive technique  is offered to those patients who have a higher risk than the general population of having a fetus with chromosomal alterations (the most frequent are Down syndrome, which is associated with three chromosomes 21; Edwards syndrome, which is associated with associated with three chromosomes 18; Patau Syndrome, associated with three chromosomes 13) and consists of taking a little amniotic fluid from the patient under ultrasound control with a long and fine needle, and after cultivating some cells, the chromosomes will be studied.

At 14 weeks of gestation, thanks to a non-invasive technique such as ultrasound, we can determine the sex of the fetus with certain guarantees. In any case, nowadays, except on rare occasions, such as the study of certain sex-related diseases (hemophilia, etc.), it is not justified to carry out an invasive technique to know the sex of the fetus, since ultrasound, A technique that does not cause any harm to the mother or the fetus, it is capable of informing about sex correctly on most occasions.