When you're making a baby, what natural things can you do to give you more chance of having a boy or a girl? Many people have debated whether there really are natural ways to choose the sex of your baby before you become pregnant, but others say the options are simply old wives' tales.
There are of course medical ways to choose whether you conceive a girl or a boy, but these are currently illegal in the UK, other than in exceptional health-related circumstances.
Here are the most common ideas about how best to conceive a boy or girl, should you wish to choose...
There are two types of sperm: the 'male' sperm, which carries the Y chromosome, and the 'female' one, which carries the X chromosome. In 1970, an American professor of gynaecology, Dr Shettles, published his book, How To Choose The Sex Of Your Baby, which introduced the theory that male sperm are fast but weak and that female sperm are slower but more resilient. Nearly 40 years on, the Shettles Method remains the most popular natural technique for conceiving a particular sex and claims a 75% success rate.
The theory relies on timing and knowing when you're ovulating. To boost your chances of conceiving a girl, you need to have sex two to three days before ovulation, as female sperm have more staying power. To increase your chances of having a boy, it's best to have sex as close to ovulation as possible.
There's still no strong scientific evidence to support Shettles' claims and a recent computer analysis of sperm failed to find the supposed differences between male and female sperm.
'Studies are few and far between,' says fertility expert Laurence Shaw of the Bridge Fertility Clinic in London. 'I suspect 75% is a bit optimistic. But there's evidence that pregnancies due to failure of the Pill are more likely to be female,' he says. 'If Shettles is right, this might be because progestagens in the Pill thicken cervical mucus. This makes the journey harder, supposedly favouring sperm with X chromosomes, which Shettles says are stronger.'
Choose your diet
A study at the University of Missouri found that mice gave birth to more females if they were fed diets low in saturated fats and high in carbohydrates. Another theory suggests that if you eat lots of calcium and magnesium-rich foods, such as dairy, spinach and wholemeal bread while you're trying to conceive, you're more likely to have a girl. This is based on the idea that there are four mineral salts in the body - calcium, magnesium, sodium and potassium - which can affect the way an egg is fertilised.
If a boy is desired, sodium and potassium-rich foods, such as meat, sausages, rice, pasta, beans and salted meat products, are the key minerals. But food high in salt is certainly not recommended. 'I wouldn't advise anyone to cut specific minerals from their diet while trying to conceive, as they might deprive the growing foetus of essential nutrients,' says nutritionist Victoria Greaves. 'You certainly shouldn't exceed the recommended daily intake of 2.5g sodium, or 6g salt.'
We spoke to one mum who believes her and her partner chose the sex of their baby through natural measures. 'After having two boys I was happy to adopt a specific diet when trying for number three,' says Beth Collins, 30, mum to Jake, 4, Matthew 2, and Rachel, 9 weeks. 'I really wanted my next baby to a girl. I read all the books and worked out the 'girly' times of the month, and informed my husband in a light-hearted way that we should give it a go. We waited until the birth to find out the sex, and I was incredibly nervous. I was so geared up for another boy, I was in absolute shock when Rachel came out!'
Medical Sex Selection
Choosing the sex of your baby by embryo selection without a medical reason, even during IVF (in-vitro fertilisation) treatment, is banned in the UK.
'After two public consultations, opinion was categorically against sex selection for non-medical purposes - what Americans call family balancing', says a spokesperson for the Human Fertilisation and Embryology Authority (HFEA). 'Around 80% of those asked in the UK objected to sex selection on both moral and ethical grounds.'
Only in extenuating circumstances, such as a family history of a serious disease that could affect a child of a certain sex, Duchenne Muscular Dystrophy in boys, for example, can medical sex selection be carried out in the UK and Europe. In such cases, a method called pre-implantation genetic diagnosis (PGD), which puts back only embryos of the required sex, is performed during the IVF process.
It's possible for British couples to receive PGD for non-medical reasons in the US, but it's expensive. Clinics, including one in London, liaise with medical facilities in America to offer this treatment. Early consultations are carried out in this country, but owing to the UK ban, medical procedures are done in the US. It costs around £12,000, excluding flights and accommodation.
Although nearly all pregnancies result in a child of the desired sex, as the treatment involves IVF, it's invasive and requires intensive hormone treatment.
Before 2007 couples were able to choose the sex of their babies by a process called sperm sorting. At the time it was legal and unregulated in the UK, and sorted X from Y sperm, with only 'male' or 'female' sperm are used for artificial insemination. There were three private clinics (in Birmingham, London and Glasgow) openly offering treatment in the UK and it cost around £4,000 for four attempts.
Government research showed a child of the desired sex was produced in 70%-90% of pregnancies using this process, but there were no guarantees, and no refunds.
From 1995 to 2007 between 150 and 200 couples a year have had the procedure in the UK.
It is now available in the US, where it's commonly called 'family balancing' and is considerably cheaper and more widely available.