Female Embryos More Likely To Die In The Womb Than Males — Study Suggests Girl Fetuses Are At A Higher Risk During Pregnancy

A new study has challenged the widely believed hypothesis that it is the males who were susceptible in the womb. It suggests that it is the female embryos who are at a higher risk during pregnancy.

When a woman gets pregnant, it is common assumption that there’s a 50-50 chance of having a boy or a girl, but multiple studies have indicated that the ratio is quite skewed. Statistics show for every 100 girls born around the world, we’ll get 103 to 107 boys. For many years, it was assumed that nature “favoring” the male child, stemmed from the “fragile male” hypothesis.

The hypothesis stated that the female embryos are generally stronger and less susceptible to health disorders or risks in the womb. Moreover, after they’re born and start growing up, girls are less likely to engage in risky, violent behavior that could get them killed. Interestingly there’s ample research to back up both of these claims.

Owing to this natural phenomenon and gender-based differences, it was accepted that that human conception results in more male than female zygotes — the cells that form when two sex cells, or gametes, are joined through sexual reproduction. This essentially gives the male gender a fighting chance. In other words, more men die due to their foolhardy heroics or dangerous life-choices and this is nature’s way of balancing the male-female ratio.

However, a new research has turned the hypothesis completely in reverse, suggesting that it is the female embryo that is more likely to die in the womb than male. Speaking on the topic, biologist Steven Orzack, who led the research at the Fresh Pond Research Institute in the U.S. said,

“This is an excellent example of an idea in science that’s had wide circulation, but where the empirical basis was ambiguous. It gets in textbooks and then it’s viral. No one really sat down and said ‘let’s try and make sense of all this'”.

Orzack’s study followed 140,000 pregnancies in the U.S., observing the growth and health of the fetuses and embryos from one week after conception, until they were born. Additionally, all the pregnancies were the result of assistive reproductive technologies, such as IVF. The team also analyzed data from almost 900,000 fetal screening tests and 30 million abortion, miscarriage and birth records, mostly from clinics in the U.S. and Canada.

Surprisingly, the results indicated nature isn’t biased, exclaimed Orzack,

“The best estimate we have is that it’s even-steven – 50 percent males [and] 50 percent females. This means the skewing must occur throughout the course of a pregnancy.”

In addition to the revelation, it was learnt that across the entire length of a pregnancy, unborn females were at a relatively higher risk of death than their male counterparts.

Exactly why the female embryos are at a higher risk isn’t clear, admitted the team,

“One possible mechanism is that a paternal X chromosome retards development in such a way that female mortality rate increases; this has been confirmed in the mouse.”

[Image Credit | Itsy Bitsy Steps]