'Is it a boy or a girl?': The midwives' myths Serena Williams needs to read

Is it a boy or a girl? Every expectant mother wants to know. To find out, some will opt for an ultrasound scan, some decide to wait until the birth – and some, like Serena Williams, will just ask their 8.63 million Twitter followers to guess.

This week, the tennis champion, who is around seven months pregnant, took to social media to share a nude photograph of her and her bump on the cover of Vanity Fair. “Question - what do you guys think, boy or girl?” she wrote. “I’m waiting to find out but would love to hear your thoughts.”

Within seconds, thousands of her followers began sharing their thoughts. “Definitely a boy,” some declared confidently. “She’s carrying low, and it’s sticking out at the front; not spread around the sides.” While others suggested her baby would be a girl, because “boys tend to look rounder and more like a bubble”. 

Old wives’ tales that claim to predict a baby’s gender have little-to-no basis in scientific reason, but some couples still swear by them. For others, they’re just fun games to pass away 40-odd weeks of pregnancy.

So, for Williams and any other future mums, here are the top seven old wives’ tales to find out* a baby’s gender (*may not work in practice).

Check your bump

As with Williams’ bump, there is much speculation on the size and shape of a woman’s stomach when she’s carrying. If it is a neat bump that sticks out and sits low, then it is a boy, while if the weight is more spread out around the mother’s middle, it’s a girl.

The reasoning is that boys, on average, weigh more than girls at birth, so the bump would be slightly bigger. But the small weight difference would not necessarily change the shape of the bump, and there is no scientific evidence to support this claim. 

Take a breast measurement

According to science writer Jena Pincott, women carrying girls develop larger breasts during pregnancy than women carrying boys. She found that busts increase by 8cm on average in mums carrying girls, compared with 6.3cm to those pregnant with boys. In her book, Do Chocolate Lovers Have Sweeter Babies?, she explained it was because male foetuses produce more testosterone, and that may suppress breast growth. 

Monitor your morning sickness

More than 80 per cent of women experience nausea in the first 12 weeks, and around half of all pregnant women experiencing vomiting. But it may not be just a myth that women who suffer particularly heavy morning sickness, including vomiting, are having a girl.

A study by Ohio State University in the US, earlier this year, showed women carrying daughters produced more pro-inflammatory cytokines - chem­icals that go overboard when bacteria is present, and can contribute to the serious sickness condition, hyperemesis gravidarum. Though it’s worth noting the Duchess of Cambridge suffered from this in her pregancies with both Prince George and Princess Charlotte.

How was conception achieved? 

The exact sexual position in which a baby was conceived is said to shed light on its gender. If a woman bends her knees during sexual intercourse, the sperm will be deposited closer to the egg. It is believed that if the male sperm reaches the egg first, a male chromosome will fertilise the egg, producing a boy.

Others suggest that if couples want a boy, they should have sex as close to ovulation as possible, as a woman’s vaginal fluids will be most alkaline, thus creating the best conditions for the male chromosome to thrive. To have a girl, couples just need to do the opposite and have sex as far away from ovulation as possible.

How goes the pregnancy glow?

Every mum-to-be wants the much-talked about pregnancy glow, where they have a bright, clear complexion and shiny hair. Bad luck if they desperately want a girl, because women carrying girls are said to have more acne and hormonal skin problems. According to the old wives’ tale, it is because “little girls steal their mums’ looks”. 

Take your blood pressure

A study published in the American Journal of Hypertension earlier this year found maternal blood pressure before a baby is even conceived could be linked to gender. Out of 1,411 women, they found that blood pressure was higher in women who went on to have a boy than those who had a girl. 

Geoffrey Trew a consultant in Reproductive Medicine and Surgery at the Hammersmith Hospital in west London, is, however, sceptical. “I’d very surprised that a BP measurement, which is notoriously variable, could dictate sex 26 weeks before pregnancy.”

Sleep on one side

According to myth, if a pregnant woman naturally sleeps on her left side, she is carrying a boy, while if she sleeps on her right side, she’s going to have a girl. However, the National Childbirth Trust (NCT) advises that, if possible, women should try and sleep on their left side, especially in later pregnancy, as it can improve blood flow and help kidneys efficiently eliminate waste products from the body. 

And if you still can’t determine your baby’s gender… try the pendulum test

Get the mum-to-be to lie on her back and to dangle a wedding ring over her stomach. The ring should be attached to a piece of string or, if she’s really committed to the test, a lock of her hair. If the ring swings in a circular motion, the theory goes, she’s having a girl; if it swings from side to side, she’s having a boy. 

“Pendulum dowsing” is said to work by tapping into the future mother’s intuition, sixth sense – or a desire for her baby to have a specific gender.