Female foetuses show sensitivity to their mothers' stress unlike the males who just ignore it, discovered scientists at the University of Adelaide in South Australia.
According to the researchers, the finding could lead to better treatments for male foetuses at risk of premature birth.
Vicki Clifton and colleagues at the University of Adelaide studied the effect of cortisol, a stress hormone produced by pregnant women, on both male and female foetuses.
The team found that baby girls exhibited higher amounts of cortisol in their cord blood, while the baby boys did not.
The team also observed that 22.5 per cent of girls born to asthmatic women were among the lightest 10 per cent of all babies born worldwide.
A smaller foetus can deal better with adversity in the womb, such as a drop in nutrients during an asthma attack, but the researchers believe there must be a reason why the male babies continue to grow at a regular pace despite these changes.
"There must be some benefit in males being bigger at birth, and this is worth the risk [of being affected by an associated drop in nutrients]," New Scientist quoted Tim Moss, a prenatal physiologist at Monash University in Melbourne, Australia, as saying.
Moss said that the work has important clinical applications that "could help us to reduce the vulnerability of male infants".