New research found that baby girls cope better with stress in their mothers' womb.
For the first time studies at the University of Adelaide's Robinson Institute have established differences in how baby girls and boys cope with stress during pregnancy.
Faced with issues like a mother smoking, drinking alcohol, suffering from asthma or having an infection, the girls appear more resilient and better able to cope with multiple events before birth.
But the news isn't all bad for boys, with the research also showing they do better than girls if the mother only faces a single stress, like asthma, or a single infection.
Professor Vicki Clifton told reporters that when mother has a stressful event during her pregnancy, baby boys will make themselves as big as they possibly can and ignore what is happening to their mother's body. On the other hand, baby girls will make themselves a little bit smaller for a greater chance of survival in case the pregnancy didn't go well.
However, Professor Clifton said that boys are likely to be at risk of delivering pre-term or worst, being stillborn if pregnancy doesn't go well.
Girls are lean and mean and they're survivors.
Professor Clifton said the explanation for the differences lay with the movement of stress hormones across the placenta.
Girls make big adjustments to the presence of stress hormones while boys try to ignore them, which could impact on their chances of making it to full term or having health issues after birth.
Professor Clifton said it was hoped her research would help better educate potential and pregnant mothers about the risks associated with habits such as smoking and alcohol use, and the possible impact on their babies.
It should also help educate women on the need to take good care of themselves during pregnancy, including watching their diet and better managing conditions such as asthma.