Want a baby girl? Keep blood pressure down, study shows

Higher systolic blood pressure signals a woman will deliver a boy while lower suggests a girl.
Higher systolic blood pressure signals a woman will deliver a boy while lower suggests a girl.NEW PAPER FILE PHOTO

TORONTO, Canada - Scientists have found that a woman's blood pressure can determine whether she has a baby boy or a girl, according to reports.

A Canadian study discovered that a woman’s blood pressure at around 26 weeks before conception can predict the sex of her baby.

Higher systolic blood pressure signals she will deliver a boy, while lower suggests a girl, said Britain's Telegraph.

Dr Ravi Retnakaran, endocrinologist at Mount Sinai Hospital in Toronto, said: “It suggests that a woman's blood pressure before pregnancy is a previously unrecognised factor that is associated with her likelihood of delivering a boy or a girl.”

The team made the connection while trying to work out what determines the ratio between girls and boys in a population, the Telegraph said.

Several studies have shown that stressful events such as wars, natural disasters and economic depression can change the proportion of boys and girls in a country.

The difference occurs because in stressful times one gender is more likely than the other to survive through pregnancy. So even though the conception sex ratio remains at 50:50, the birth ratio will alter depending on which sex is stronger.

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

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

“What is believed to vary is the proportion of male or female foetuses that is 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 foetus or that higher blood pressure before pregnancy is less conducive to survival of a female foetus.

“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, 1,411 newly-married Chinese women were recruited all who were trying to become pregnant. Their blood pressure was checked at around 26 weeks before conception and they were followed through pregnancy. Overall, the women gave birth to 739 boys and 672 girls.  

After adjustment for age, education, smoking, Body Mass Index (BMI) , waist, cholesterol, triglycerides 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 Prof Charles Kingsland, of Liverpool Women’s Hospital, said: “We have been aware that more male foetuses miscarry than females and more females are born for obvious biological reasons, namely you need more women in the world to have children.

“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 conception of different sexes.

“This study is, therefore, very interesting. However, it does not take into account the potential physiological aspects of race. Will those changes be the same in the Caucasian or Afro-Caribbean populations in the world. And what if you want a girl? Do you just go and live in Syria for a few months?”

However, some experts were sceptical about the results, the Telegraph said.

Geoffrey Trew a consultant in Reproductive Medicine and Surgery at the Hammersmith Hospital in west London said: “I haven't heard anything like this before.

“I would be very surprised that a BP measurement , which is notoriously variable, could dictate sex 26 weeks before, some reptiles can have sex differences due to temperature changes at the time of early foetal growth , but not 26 weeks beforehand.”

The study was published in the American Journal of Hypertension.