Chloe and Richard have three sons. They are trying for another baby, but Chloe desperately wants a girl this time. Richard, meanwhile, is happy with their brood of boys.

Chloe says “I want a girl so badly it is consuming my every waking moment. I know I am lucky to have three healthy, beautiful boys, but I can’t bear the thought of getting pregnant again with another one. I know this attitude is incredibly spoilt. I’m ashamed to talk to my friends about it, as many of them are struggling to conceive even one child. But there it is – the truth. I am trying anything that websites and books recommend to help conceive a girl, but there’s so much conflicting information. The advice I’ve been following so far is: limiting when we have sex before ovulation, trying to have deeper penetration, eating only alkaline foods and douching with lemon juice and vinegar, although I’m confused about that, because I also read that it should be bicarbonate of soda.”

Richard says “I would happily have more boys, or even a whole football team. At 38, Chloe is panicking that she won’t ever have a girl. I tell her that this obsession is madness, and that we should just be enjoying our lives and what we have. But it’s got to the point where she won’t have an orgasm because it may mean having a boy. She’s forcing me to wear tight underpants and to take hot baths – all to get a girl. Last week, having read something on a website, she mentioned ice, but I drew the line at that.”

Zita’s advice It all sounds exhausting. Chloe, at 38, you cannot afford to limit your window of fertility. You run the risk of not getting pregnant at all. There are many books on the subject of sex selection, but the fact is that there is no reliable scientific evidence to support the theories such sources may suggest.

It has not been soundly proven that intercourse on the limit of the fertile time increases the chances of having a girl, while sex closer to ovulation may help to conceive a boy. As for douching with lemon juice and vinegar, it sounds painful and is definitely best avoided. As you get older, your oestrogen levels drop, which, in turn, diminishes cervical secretions. These secretions form channels for sperm to swim up – so the less there is, the more difficult the swimming. Books offer contradictory advice, saying that acidic conditions help a woman to conceive a girl and alkaline conditions a boy, but an acidic douche wastes valuable secretions, so it is counterproductive.

When it comes to diet, you need to remember that food is a pleasure that should nourish us on every level. There are far too many food fascists around today. I do, however, encourage my clients to eat an alkaline-rich diet (asparagus, melon, mango) and just a small amount of acidic foods (tomatoes, red meat, refined pasta and so on), as there is a small amount of research to indicate that an overly acidic diet may hinder the embedding of the embryo. This is a matter of maintaining good health, not influencing the sex of your child. As for Richard, tight pants and hot baths are an absolute nono. You may well end up with hardly any sperm if you continue with these tactics.

The most frequently quoted study on determining a baby’s sex is the Shettles theory, but its results are not wholly convincing. Dr Landrum B Shettles based his study on sperm’s swimming ability and stamina, and whether it was in contact with an acidic or alkaline vaginal environment. As Y-bearing (male) sperm are lighter and swim faster in the reproductive tract than heavier, slower X-bearing (female) sperm, it was thought that intercourse closer to ovulation increased the chances of conceiving a boy (as male sperm swim faster, but have a shorter life span) and intercourse on the limits of the fertile time increased the chances of a girl. This study included 22 couples trying for a boy, of whom 19 were successful, and 19 couples trying for a girl, of whom 16 were successful. However, as it was a small study, and took place more than 30 years ago, it cannot be considered evidence-based research.

A review of six studies in the early 1990s failed to confirm the Shettles theory. Similarly, a study in New Zealand found completely the opposite results. Large, well-conducted trials failed to determine a link between intercourse timing and sex difference. Quite simply, there is no guaranteed way to choose the sex of your baby naturally.

I am against the idea of sex selection, in principle, and it is illegal in this country. However, various methods are available in America and, as you are intent on knowing all the options, I will explain the two main processes. But please consider the implications carefully.

Option 1: Sperm sorting

This is a way of separating male and female sperm. The latest method on trial is called Microsort. It is based on the fact that the X chromosome has greater mass than the Y chromosome because of its higher total DNA content. Once the man has produced a sample, the sperm are sorted by DNA analysis and those of the appropriate gender are then used for intrauterine insemination to fertilise the woman’s egg. The Genetics and IVF Clinic in Fairfax, Virginia, which is researching Microsort, has an 88% success rate for couples wanting girls and a 73% success rate for boys. But be warned: there are concerns about the lack of published data on this technique and the fact that the procedure may change the unborn baby’s DNA, which might cause long-term health problems for the child.

Option 2: Preimplantation genetic diagnosis (PGD)

This involves a couple undergoing IVF. In PGD, a single cell is taken from the embryo and tested in the laboratory. The embryo(s) of the chosen sex are then placed back into the woman’s body and the others are discarded. The Human Fertilisation and Embryology Authority allows sex selection only for couples who carry a genetic condition that would be passed on to a child of a particular sex.

If you still wish to find out more, Professor Frank Comhaire, in Ghent, Belgium, is well known in this field. He will be able to advise you and do the relevant tests, although he no longer performs sex selection in Belgium. In the past six years, he has had a 95% success rate, working with 60 couples. E-mail him at frank@comhaire.be. For more about Microsort, visit www.microsort.net

Zita West is widely recognised as London’s leading holistic pregnancy and fertility guru. She has been a midwife for 25 years and is also a qualified acupuncturist and nutritional therapist. West runs a holistic pregnancy and fertility clinic in central London and is the author of several books on fertility

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