A new study suggests it’s possible to determine the sex of a baby even before it has been conceived. Of course, that’s not a new concept – old wives' tales have suggested everything from pregnancy cravings to ancient Chinese lunar charts can predict a baby’s sex, but scientists in Canada have discovered there could be a more accurate physiological marker: blood pressure.
The researchers were studying what determines the ratio of boys to girls in a population when they discovered that weeks before even conception, whether a woman’s blood pressure was high or low was a good indicator of whether she would conceive a girl or boy. They found that higher systolic blood pressure tended to result in boys, while lower blood pressure resulted in girls.
Previous studies have demonstrated how times of war and other stressful events such as economic depression or natural disasters can affect the proportion of boys and girls born in a localized region. Though the reasons are unclear, scientists suspect more boys are born during these times as the fetuses may be stronger and survive through pregnancy, making the conception ratio still 50:50 but the actual birth rate slightly skewed.
The new study, led by Dr. Ravi Retnakaran of Mount Sinai Hospital in Toronto and published in the American Journal of Hypertension, involved monitoring 1,411 women who were planning a pregnancy. They were assessed at an average of around 26 weeks prior to pregnancy. These pregnancies resulted in 739 boys and 672 girls.
After adjusting for age, education, smoking, BMI, cholesterol, triglycerides, and glucose, the study results revealed that the women who went on to have boys had higher systolic blood pressure at 26 weeks, compared to those who had lower blood pressure and went on to have girls.
"[This] suggests that a woman's blood pressure before pregnancy is a previously unrecognized factor that is associated with her likelihood of delivering a boy or a girl," Retnakaran announced in a statement. "This novel insight may hold implications for both reproductive planning and our understanding of the fundamental mechanisms underlying the sex ratio in humans."
One of the most controversial implications of this discovery is whether or not women will be able to influence the gender of their baby by deliberately elevating or lowering their blood pressure, something that could be desirable in societies who favor boys being born. The study did not address this though, perhaps for that very reason.