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Having three children of one sex is a mere statistical quirk
</div> 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 for social reasons.
IVF clinic consultants, like Dr Bowen-Simpkins, do get many queries about sex selections from parents of a number of children of one sex, particularly from Asian parents who have had several girls and want a boy.
WHO, WHAT, WHY?
A part of BBC News Magazine, Who, What, Why? aims to answer questions behind the headlines
But the typical circumstances where sex selection is allowed is where a serious inherited disease particularly affects one sex. One of the most common is Duchenne muscular dystrophy, which usually affects boys.
In other countries the rules are less strict and sex selection takes place, particularly in case of in-vitro fertilisation.
And whatever the scepticism about boy or girl-only families being anything more than a statistical quirk, there is nothing to say that in the future science won't establish that there is an explanation.
"If you can physically separate sperm [in a lab] you can imagine biological environments where this can happen naturally, in the woman's reproductive tract. But I've never seen any evidence that it is the case," says Prof Fleming.
This article is from the BBC News website. © British Broadcasting Corporation, The BBC is not responsible for the content of external internet sites.
Having three children of one sex is a mere statistical quirk </div> 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 for social reasons.
IVF clinic consultants, like Dr Bowen-Simpkins, do get many queries about sex selections from parents of a number of children of one sex, particularly from Asian parents who have had several girls and want a boy.
WHO, WHAT, WHY?
A part of BBC News Magazine, Who, What, Why? aims to answer questions behind the headlines
But the typical circumstances where sex selection is allowed is where a serious inherited disease particularly affects one sex. One of the most common is Duchenne muscular dystrophy, which usually affects boys.
In other countries the rules are less strict and sex selection takes place, particularly in case of in-vitro fertilisation.
And whatever the scepticism about boy or girl-only families being anything more than a statistical quirk, there is nothing to say that in the future science won't establish that there is an explanation.
"If you can physically separate sperm [in a lab] you can imagine biological environments where this can happen naturally, in the woman's reproductive tract. But I've never seen any evidence that it is the case," says Prof Fleming.
This article is from the BBC News website. © British Broadcasting Corporation, The BBC is not responsible for the content of external internet sites.
