Boy or girl? 56% of IVF babies are MALE – and now doctors know the surprising reason why

Most expecting parents believe their chances of having a boy or girl are 50/50.

However, according to scientists, those who undergo in vitro fertilization treatment are more likely to have a boy.

Experts found that male embryos grow slightly faster and are therefore more likely to be transferred to the uterus.

And this may explain why the odds of having a boy through in vitro fertilization are as high as 56 in 100.

Fertility expert Dr. from University College London. “When you equate faster with better, you’re favorably selecting for male embryos,” said Helen O’Neill. ‘The tools we use choose men.’

Male embryos have one X and one Y chromosome, while female embryos have two X chromosomes.

One of the X chromosomes is turned off in the earliest stages of development; This is a crucial mechanism for genetic balancing, but it requires energy and resources.

Since embryos are selected based on how well they grow and develop, male embryos are more likely to be selected because they grow slightly faster in the first few days after fertilization.

Previous studies had found that in vitro fertilization slightly increased the chances of having a boy, but scientists weren’t sure why.

Dr O’Neill said the explanation for this might be that the process of growing the embryos in a container made the male embryos more likely to survive.

But the new study, presented at New Scientist Live and reported in the journal I -Suggests that gender bias occurs when embryos are selected for transfer.

Traditionally, doctors always grade embryos for quality by looking at them through a microscope.

Some fertility clinics are now also offering the use of artificial intelligence as part of the sorting process, using time-lapse videos of embryos as they develop.

Dr O’Neill’s team conducted a study to determine the likelihood of male or female embryos being selected by both doctors and two different artificial intelligence systems. They tested 1,300 embryos whose gender was already known through genetic testing.

The analysis found that when doctors made the selection, they rated 69 percent of male embryos and 57 percent of female embryos as good quality.

One of the AI ​​systems had a slight gender bias towards males, while the other evaluated male and female embryos almost the same.

During IVF, sperm is added to several eggs in a dish in the hope of creating as many embryos as possible. After approximately five days, the healthiest looking embryo is selected to be transferred to the uterus.

Dr O’Neill said the difference in development rate was so small that it could not be used to consciously select male or female embryos.

Gender selection is also not allowed during IVF in clinics in the UK unless the parents have a genetic medical condition that affects only one gender.

A previous study by scientists at Harvard University found that some women are much more likely to have children of only one gender.

For their study, the team analyzed data from more than 58,000 mothers who had given birth to at least one child. The results revealed that maternal age plays an important role in determining the sex of babies.

Women who were over 28 when they first gave birth had a 43 percent chance of having a single-sex child.

But women who were under 23 when they became mothers for the first time had only a 34 percent chance of having a single-sex child.

“Older maternal age may be associated with a higher likelihood of having a single-sex child, but other hereditary, demographic, and/or reproductive factors were not associated with the sex of the child,” the researchers explained.