Is there a difference in the embryo developing according to gender?

Is there a difference in the embryo developing according to gender?

Patients undergoing an in vitro fertilization treatment usually ask if are able to distinguish between male and female embryos while observing them in the lab.

Can we know the embryo gender before implantation in the mother’s uterus?

Although the embryo’s gender is established at the time of the egg and sperm union, is not until week 5, approximately, when the embryo develops according to its gender. Until this moment, the embryo is in a phase known as sexual development undifferentiated term. This means that by only observing the embryo in the lab we are no table to know its gender.

Embryo behaviour according to gender

A few years ago, time-lapse equipment were introduced in the in vitro fertilization field, these are high resolution cams which allows to continuously observe the embryo. This advantage let us go into detail about the embryo’s evolution study in shape and speed. It was then when the first publications observed that there were differences in the division speed between sexes. At present, many studies conclude that some division stages are faster in male embryos.    

This phenomenon has an explanation, female embryo cells have two copies of chromosome X, whilst males only have one copy. A compensation that makes both sexes to have same expression or chromosome reading is needed. This compensation makes female embryos to inactivate most of one of the X chromosomes genes, this is, annuls the Reading. This phenomenon is called X chromosome inactivation. As male embryos do not have to perform this process, this means they can carry out a faster division at some developing stages.

Statistics predictibility

Taking advantage of this phenomenon, different models to analyse the embryo’s division speed have been generated to predict its gender. But this is not an exact proof so, the only method to know the embryo’s gender with certainty is by analysing its genetic charge (PGD). We have to point out that the Spanish legislation states that selecting a baby’s sex is only allowed with a view to avoiding the transmission of genetic diseases associated with the sexual chromosomes.


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