Sexual Inequality Between Boys And Girls Starts In The Mother's Womb

Male and female twin polar bear babies in Munich, Germany. Alexandra Beier/Getty Images

Sexual inequality between boys and girls starts as early as in the mother’s womb, according to new research.

The girls are clearly ahead in the survival stakes but until now we weren’t sure why.

A team from the University of Adelaide’s Robinson Research Institute has been studying the underlying genetic and developmental reasons why male babies generally have worse outcomes than females.

The results, published today in the journal Molecular Human Reproduction, show that male and female babies develop in very different ways and the placenta plays a key role in these gender differences.

“Our research has found that there are undeniable genetic and physiological differences between boys and girls that extend beyond just the development of their sexual characteristics,” says senior author of the paper Professor Claire Roberts, leader of the fetal growth research priority for the Robinson Research Institute.

“We’ve known for some time that girls are clearly winning in the battle for survival, with markedly better outcomes for female babies for preterm birth, stillbirth, neonatal death, and other complications after birth,” he says.

“Male babies generally grow faster and bigger than females. This occurs in both the animal and human worlds, but until now we haven’t really understood how or why.”

The researchers investigated whether the type and pattern of genes being expressed by the placenta is different for boys and girls.

“Our results suggest that there is a distinct sex bias in the regulation of genes in the human placenta,” says lead author and University of Adelaide PhD student Sam Buckberry.

“We found that with female babies, there is much higher expression of genes involved in placental development, the maintenance of pregnancy and maternal immune tolerance.

“This suggests that girls are more likely to adopt a risk-averse strategy towards development and survival, and it goes some way to explaining the differences in male and female development in the womb.”

The findings may be important to help guide future sex-specific therapeutics for pregnant women and for babies in the nursery.

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