Craving sweets, early morning sickness and a watermelon-shaped stomach are all said to indicate that a woman will give birth to a baby girl.
But an intriguing new study suggests that a woman’s blood pressure before she gets pregnant could affect whether she has a boy or a girl, scientists have claimed.
Researchers found those with lower blood pressure tended to have a girl, while higher blood pressure was an indication that a boy was more likely to be conceived.
It was unclear whether a woman who wanted to have either sex could influence the outcome by deliberately raising or lowering her blood pressure.
The issue is controversial because of the practice of gendercide -in which female babies are aborted or even killed after birth -in some male-dominated societies.
One of the researchers, 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.”
“This novel insight may hold hold implications for both reproductive planning and our understanding of the fundamental mechanisms underlying the sex ratio in humans,” Dr Retnakaran said.
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.
Those who had a female child had an average systolic blood pressure of 103.3mmHg before pregnancy, while for mothers of males the figure was 106, about 2.6 per cent higher.
Fundamental biology means there is generally a 50/50 split in the sex ratio, although in humans there is a slight bias towards males. This is seen as nature’s way of balancing out their slightly higher risk of premature death.