Women carrying a boy are more likely to experience complications and possibly life-threatening outcomes during pregnancy than those carrying a girl, according to a new study released today.
The research, led by the University of Adelaide, investigated the data of more than 574,000 South Australian births over a space of 30 years to determine whether gender matters when it comes to pre-term births, pregnancy-induced high blood pressure disorders, and gestational diabetes mellitus.
The study found that boys are more likely to be born spontaneously premature than girls, as male babies have a 27 per cent higher risk of being born very early, between 20-24 weeks' gestation.
“This means that for every 100 girls born at 20-24 weeks gestation, there’s also 127 boys born at 20-24 weeks gestation,” explains research leader and senior author Professor Claire Roberts, from the University's Robinson Research Institute.
“A woman is more likely to have issues during pregnancy if her baby is a boy because she is more likely to deliver her baby pre-term, more likely to have gestational diabetes and more likely to have pre-eclampsia at term."
The research shows that male babies have a 24 per cent higher risk of being born pre-term at 30 to 33 weeks gestation compared to female babies.
A pre-term birth puts the baby at risk of both short and long-term health concerns - from infections and vision problems to intestinal issues - depending on how early the baby is born.
Mothers carrying boys are also four per cent more likely to suffer gestational diabetes and 7.5 per cent more likely to suffer pre-eclampsia at term.
However, the study shows that pregnant women carrying a girl have a 22 per cent higher risk for early onset pre-eclampsia requiring a pre-term delivery.
"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.
“...A woman is more likely to have issues during pregnancy if her baby is a boy because she is more likely to deliver her baby pre-term, more likely to have gestational diabetes and more likely to have pre-eclampsia at term.
“This is because there are genetic reasons that underline pregnancy complications.”
According to The Women’s - The Royal Woman’s Hospital in Victoria, pre-eclampsia is the most common serious medical disorder of human pregnancy in Australia: mild pre-eclampsia occurs in five to 10 per cent of pregnancies and severe pre-eclampsia in one to two per cent of pregnancies. It can cause the pregnant woman to have high blood pressure, kidney dysfunction and difficulties with vision. It can be life threatening for both mother and baby if left untreated.
“But these findings don’t mean that women should worry about carrying a boy.
“What we know now is that genes don’t act in isolation: they are also effected by the environment. So our message to women is that they should take care of themselves during their pregnancy and get a good amount of exercise, avoid smoking cigarettes and marijuana, and avoid drinking alcohol.”
“But these findings don’t mean that women should worry about carrying a boy. What we know now is that genes don’t act in isolation: they are also effected by the environment."
The research, published online in the journal PLOS ONE, marks the first study of its kind in Australia to confirm that birth outcomes are related to sex.
Professor Roberts says no one knows the reason why the relationship exists. However, the differences in male and female placentas, which are critical for pregnancy success, could play a significant role.
“The next step is to understand the consequence of these differences and how they influence the path to pregnancy complications."
Lead author Dr Petra Verburg from the University of Groningen, also currently based at the University of Adelaide's Robinson Research Institute, adds that more research is needed to determine how these findings could be used to create gender-based pregnancy complication treatments in the future.
“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,” says Dr Verburg.
“We're investigating other factors that may predict pregnancy complications, taking foetal sex into account."
The research was conducted by University of Adelaide's Robinson Research Institute, University of Groningen in The Netherlands, and the Pregnancy Outcome Unit of SA Health.
A previous study released this year, also led by University of Adelaide researchers, shows that pregnant women who continue to use marijuana until 20 weeks gestation are five times more likely to give birth to a premature baby than women who don’t use the drug at all.
The study also found that 12 per cent of pregnant women tested in Australia used marijuana either before or during pregnancy.