Researchers from the University of Adelaide have determined that girl babies develop more cautiously in the womb and therefore have less pregnancy complications than boys.
They investigated whether the type and pattern of genes being expressed by the placenta is different for boys and girls to determine why male babies generally have worse outcomes than females, with significantly increased rates of pregnancy complications and poor health outcomes for males.
The team from the University of Adelaide's Robinson Research Institute 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," 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," he says.
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.