"Snips and snails, and puppy dogs tails..." So goes the popular 19th century nursery rhyme regarding what little boys are made of. Girls, on the other hand, get the "sugar and spice and everything nice" treatment.
The lyrics have long been deemed sexist and controversial, but strangely, the writers may have been onto something: According to a new study, boys apparently start causing trouble while they are still in the womb.
After analyzing close to 600,000 births in Australia from 1981 to 2011, researchers have found that serious pregnancy complications are more likely when women are carrying baby boys. Not only were they were more likely to be born early—compared to girls, boys had 27 percent higher odds of preterm birth between 20 and 24 weeks' gestation; 24 percent greater risk for birth between 30 and 33 weeks; and 17 percent higher odds for delivery at 34 to 36 weeks—but gestational diabetes was 4 percent more likely in women carrying boys, and preeclampsia at term was 7.5 percent more likely. Whoa!
"The sex of the baby has a direct association with pregnancy complications," said study author Petra Verburg, M.D., of the Robinson Research Institute at the University of Adelaide in Australia. She added that while it isn't totally clear why, "there are likely to be genetic factors."
One possible explanation, according to her co-author Claire Roberts, another researcher at the Robinson Research Institute, is that the placenta (which nourishes the developing fetus) is different in boys and girls.
"The placenta is critical for pregnancy success," Roberts said. "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."
That way, different care can hopefully be provided to different women one day, depending on the sex of their unborn baby. "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," Dr. Verburg explained. "We're investigating other factors that may predict pregnancy complications, taking fetal sex into account."
In the meantime, the advice for women carrying boys remains the same as for all pregnant women—eat right, stop smoking, get exercise. "Even if the pregnancy was unplanned," Dr. Verburg said, "there is still a window of opportunity for a woman to reduce her risks for pregnancy complications."