A study by a team of researchers in Canada and China suggests that maternal blood pressure before conception may influence the gender of a child. According to the study, women who delivered a male child had higher blood pressure before pregnancy compared to those who delivered a female child.

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The study, titled "Maternal Blood Pressure Before Pregnancy and Sex of the Baby: A Prospective Preconception Cohort Study," "shows an association between a woman's blood pressure before pregnancy and her likelihood of delivering a boy or girl after she becomes pregnant," said Dr. Ravi Retnakaran of Mount Sinai Hospital, Toronto.

The study also provides novel insights that a woman's blood pressure may be a previously unrecognized indicator of maternal factors that contribute to the sex of her child, he added.

The team of seven researchers suggested that adverse societal conditions may affect fetal viability in a sex-specific manner and thus modify sex ratio. In other words, there may be certain physiologic features related to the likelihood of a woman delivering a boy or a girl.

For the study, around 1,400 newly-married women in Liuyang, China, were chosen. Their cardiometabolic characterisation including cholesterol, blood pressure, triglycerides, and glucose was monitored approximately 26 weeks before conception and during pregnancy till delivery. A total of 739 women had boys while the rest 672 delivered daughters. The study showed that the systolic blood pressure before pregnancy was higher in women who delivered a son than in those who had a daughter. 

The study was published in the latest issue of American Journal of Hypertension.