They already have a reputation for being naughtier and noisier than their sisters.
But now it seems that boys are more difficult from the very start.
Research shows that pregnant women are much more likely to suffer life-threatening complications when they are carrying a boy rather than a girl.
These range from premature births to diabetes and pregnancy-related blood pressure problems.
The Australian researchers said that providing different care to women, depending on the sex of their unborn baby, could be better for both mother and child.
The team from the University of Adelaide crunched data on almost 600,000 births that took place over 30 years.
This revealed that boys were up to 27 per cent more likely to be born prematurely.
In Britain, one in 13 babies is born prematurely - defined as before 37 weeks of pregnancy.
Those that survive face a host of health problems, with one in ten developing a permanent disability such as lung disease, cerebral palsy, blindness or deafness.
Women carrying boys were also 4 per cent more likely to develop gestational diabetes.
This form of diabetes usually develops in the second half of pregnancy and goes away after the baby is born.
But it can have serious consequences for mother and child, including raising the odds of a caesarean section, birth defects and stillbirths.
Both woman and child are also at higher risk of developing full-blown diabetes in later life.
Finally, having a boy raised the odds of developing pre-eclampsia, a blood-pressure related disorder that can be fatal to mother and child, at the end of their pregnancy.
However, women carrying girls didn’t get off scot-free. They were more likely to develop pre-eclampsia earlier in their pregnancy.
Lead researcher Professor Claire Roberts said: ‘The major conclusion of our study is that the evidence is there and it is very clear: the sex of the baby has a direct association with pregnancy outcomes.
Colleague Dr Petra Verburg, who holds posts in Adelaide and in the Netherlands, said: ‘Our results indicate there may be a need for specific interventions tailored to male and female babies, to prevent adverse outcomes for both child and mother.
‘We’re investigating other factors that may predict pregnancy complications, taking foetal sex into account.’
Writing in the journal PLOS ONE, the team said it is possible that differences in the placenta, the lifeline that provides the baby with oxygen and nourishment as it grows in the womb, explain the phenomenon.
It is known that more than 100 differences in the genes of placentas that nurture male and female babies.
Professor Roberts added: ‘The placenta is critical for pregnancy success.
‘We believe that sex differences in placental function may explain the differences we’re seeing in outcomes for newborn boys and girls, and their mothers.
‘The next step is to understand the consequence of these differences and how they influence the path to pregnancy complications.’
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