Have you only had girls or boys? It is no coincidence, according to this study

According to a United Nations report, He is born a little more boys than girls On earth, 106 boys for 100 girls. However, we all know siblings composed only of girls or only boys.

Why BARRY, ROBIN and Maurice GIBB, do the Bee Gees have not a sister? Like the three Hemthworth brothers (Liam, Chris and Luke)? Why do these families not respect the world, almost equitable?

The biological sex of a child could he not not be as random as we thought So far? This is suggested by a study by Harvard University (United States), published on July 18, 2025 in the journal Science Advances.

Never three without four?

The researchers examined more than 146,000 pregnancies of 58,000 women, all nurses, between 1956 and 2015 in the light of eight characteristics (size, BMI, hair colors, blood groups, age at the birth of the first child, etc.).

They discovered that Some families presented more likely to have children of the same sex. And mothers having had three or more children were more likely to have only boys or only girls.

If you have had two or three girls and try to have a boy, know that your chances are not equal. You are more likely to have another girl.

According to the calculations of the researchers, the families of three boys have 61 % additional opportunities to have a fourth boy. In those of three girls, they statistically have a probability of 58 % that the fourth child is of female sex.

The biological changes linked to the age in question?

According to the study, maternal age could also play a role in the sex of a child. Women who gave birth to their first child after 28 years were slightly more likely to have only boys or girls.

According to Jorge Chavarro, it could be linked to biological changes Age linked in women (shorter follicular phase, vaginal acidity, etc.).

A shorter follicular phase would tend to promote the survival of the Y chromosome, while a more acid vaginal environment would promote the survival of the X chromosome. And each woman can present a predisposition to one or the other of these factors.

Genes that would promote non-mixing siblings

These works have also highlighted two genes that could influence having only girls or only boys.

We ignore why these genes would be associated with sex at birth, but they are, which opens up new questions.

The scientist, however, recommends that future studies are looking into the lifestyle, food and exposure to chemicals. Can these factors influence a child’s biological sex?

With health destination.

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