Why girls are better at surviving birth found

Male and female babies develop in very different ways, and the placenta plays a key role in these gender differences, according to a new study which may help explain why boys are more likely to be born preterm, stillbirth or suffer neonatal death.
Researchers from the University of Adelaide's Robinson Research Institute are studying the underlying genetic and developmental reasons why male babies generally have worse outcomes than females, with significantly increased rates of pregnancy complications and poor health outcomes for males.
The results 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," said senior author of the paper Professor Claire Roberts, leader of the foetal 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, such as macrosomia (a baby that weighs more than 4-4.5kg at birth).
"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," Roberts said.

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

They compared the genes expressed in 300 placenta samples and found that more than 140 genes were expressed differently across male and female samples.
"Our results suggest that there is a distinct sex bias in the regulation of genes in the human placenta," said 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," he said.
The study was published in the journal Molecular Human Reproduction.