Having three children of one sex is a mere statistical quirk Tuesday, 11 January 2011
Are the Beckhams more likely to have another boy?
Having three children of one sex is a mere statistical quirk Victoria and David Beckham are expecting their fourth child, but does having three children of one sex mean your next one is likely to be of the same sex?
The Beckhams already have three boys - Brooklyn, 11, Romeo, eight, and Cruz, five. It's a situation where many families hope for a girl, or a boy if they have had only girls.
And there are plenty of unscientific anecdotes from families who insist they are capable of having babies of only one sex. But what are the real odds?
"The odds are just about 50-50. It's like tossing a coin," says Peter Bowen-Simpkins, medical director at the London Women's Clinic, and a spokesman for the Royal College of Obstetricians and Gynaecologists.
"There is a slight preponderance of males, but it is only about 1% or 2%. There is a much higher chance of male foetus miscarriage."
So you end up with a birth rate that it is close to 50/50.
The sex of the baby is determined entirely by sperm. There are sperm that produce a boy (with a Y-chromosome) and those that produce a girl (with an X-chromosome).
THE ANSWERThe chances will be roughly 50/50, even after three boysMany claim there are ways to naturally influence sex, but fertility experts think it unlikely they make a huge difference
And the 50/50 odds are the same for any family, even one with three boys or three girls, says Prof Richard Fleming, scientific director of the Glasgow Centre for Reproductive Medicine and a member of the British Fertility Society.
Even a family of five or six boys proves nothing.
"When you have millions of families you have a wide range of standard statistical imbalances," says Prof Fleming. "I've seen some data that suggests there are seasonal elements, but the sceptics among us take that with a pinch of salt."
There are popular books giving advice on ways to be more likely to have a baby of one sex, most notably that by the fertility expert Landrum Shettles. And you will hear stories that the father's diet, timing of sex, seasonality, and even acidity and alkalinity within the female reproductive tract, can affect the outcome.
But if there is any difference to the likelihood of boy or girl it is minimal, Dr Bowen-Simpkins suggests.
"All these things will make a difference only of 1% or 2%. If you look at three generations of a family you will find it comes out pretty well 50/50."
More boys are conceived than girls Prof Fleming is also not convinced.
"I've heard a number of anecdotes based on the credentials of sperm, but hard evidence is negligible," says Prof Fleming.
Of course, you can select the sex of your baby. There is a process by which male-producing and female-producing sperm can be separated, and it is done in some parts of the world, says Prof Fleming.
But sex selection is illegal in the UK f
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