When a mother discovers that she is pregnant, one of the first things that may cross her mind is whether the baby will be a boy or a girl. That's also a consideration by doctors, but for very different reasons.
According to research made public on Thursday from the University of Cambridge, researchers have determined that the gender of a fetus may have an effect on what type of pregnancy complications await the mother. In the case of boys, they run a risk of becoming susceptible to restrictions affecting fetal growth. As for girls, mothers face a greater risk of experiencing high blood pressure as well as damage to the kidneys and liver in a condition called preeclampsia.
The research was based on findings at the Department of Obstetrics and Gynaecology, NIHR Cambridge Biomedical Research Centre, involving samples of blood and placenta tissue from around 4,000 first-time mothers.
"In pregnancy and childbirth, the sex of the baby is at the forefront of many parents' minds, but we do not even think of the placenta as having a sex," said Professor Gorden Smith, who headed the project. "This work shows that the placenta differs profoundly according to sex."
The clues to how fetal gender can affect potentially different pregnancy complications lie in molecules called "spermines," a material responsible for metabolism that is found in the mother's placenta. During the course of the research, scientists discovered that spermines are part of the genetic code geared towards the placenta, which can alter its makeup to accommodate the baby's gender.
One notable gender difference was that placentas geared towards female fetuses had more enzymes responsible for creating spermine than those for males. This might make males more vulnerable to the effects of any drugs taken by the mother that might inhibit the production of spermine, which in turn hampers metabolism and increases the risk of limited fetal development.
On the other hand, higher spermine levels in the placenta altered for female fetuses carries a different set of complications altogether. The higher levels leading to preeclampsia could be related to the observation that these newer blood vessels are narrower than what you'd find in the rest of the mother's body, which cuts down blood flow and increases the potential for high blood pressure and organ damage. But if levels of spermine are unusually low for a female fetus, the potential for compromised growth and development would be the same as what might affect boys.
"These differences alter elements of the composition of the mother's blood and may even modify her risk of pregnancy complications," said Smith. "Better understanding of these differences could lead to new predictive tests and possibly even new approaches to reducing the risk of poor pregnancy outcome."