Predicting baby’s sex

Pre-conception blood pressure could be key

Scientists in Toronto have discovered that a woman’s blood pressure at around 26 weeks before conception indicates if she will give birth to a boy or a girl.

Higher systolic (maximum) blood pressure signals she will deliver a boy, while lower pressure suggests a girl.

Ravi Retnakaran, an endocrinologist at Mount Sinai Hospital, said: “It 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.”

In the study, the mean systolic blood pressure for women who had boys was 106mm Hg, compared to 103mm Hg for those who had girls, in the months leading up to conception.

“When a woman becomes pregnant, the sex of a fetus is determined by whether the father’s sperm provides an X or Y chromosome and there is no evidence this probability varies,” added Retnakaran.

“What is believed to vary is the proportion of male or female fetuses lost during pregnancy. This study suggests that either lower blood pressure is indicative of a mother’s physiology that is less conducive to survival of a male fetus, or that higher blood pressure before pregnancy is less conducive to survival of a female fetus.

“This novel insight may hold implications for both reproductive planning and our understanding of the fundamental mechanisms underlying the sex ratio in humans.”

For the study, published in the American Journal of Hypertension, more than 1,400 newly married Chinese women were recruited, all of whom were trying to become pregnant. Their blood pressure was checked at around 26 weeks before conception and they were followed through pregnancy.

After adjustment for age, education, smoking, Body Mass Index (BMI), waist, cholesterol, triglycerides (fat in the blood) and glucose, mean systolic blood pressure before pregnancy was found to be higher in women who subsequently had a boy than in those who delivered a girl.

Fertility expert Charles Kingsland of Liverpool Women’s Hospital in England, said: “We have been aware that more male fetuses miscarry than females. There is also some evidence that you are more likely to miscarry a boy when you are compromised either by health or environmental issues. So I suppose, blood pressure changes in these circumstances might affect the conception of different sexes.” However, Kingsland noted the study did not examine potential impacts of race.

Geoffrey Trew, a consultant in reproductive medicine at Hammersmith Hospital in London, cast further doubt on the findings.

“I would be very surprised that a BP measurement, which is notoriously variable, could dictate sex 26 weeks before.”