Here's a teaser: what do Posh Spice, Jules Oliver and the one-time Hear'Say star Kym Marsh have in common? Just to narrow it down, it's got nothing to do with their celebrity, and everything to do with their fertility. The answer is polycystic ovary syndrome (PCOS).
When Victoria Beckham's pregnancy was announced at the weekend, the scary-sounding condition found its way into the tabloids, with friends divulging that Posh had feared Brooklyn would never have a brother or sister.
It was the same when the news broke last summer that Naked Chef Jamie Oliver and his wife Jules were experiencing problems conceiving because she was suffering from PCOS. And with Marsh saying Hear'Say had to alter its routines because she was in such pain, and freely confessing that she didn't know if she could have another child, you'd be forgiven for thinking it was the latest celebrity disorder.
The more prosaic truth, however, is that PCOS is far from exclusive. In fact, it affects up to one in five women in Britain. Sometimes dismissed by unsympathetic GPs, it is the most common hormonal disturbance among women and the most common cause of not ovulating. It is treatable, but there is no cure.
PCOS prevents women from ovulating or from ovulating regularly because the follicles containing the egg don't develop fully. Instead of passing into the fallopian tubes to be fertilised - as they would do normally - the immature follicles, or cysts, which measure 2-8mm compared to the 20mm developed follicles, remain in the ovary and eventually wither away to be replaced by others.
An ovary is designated "polycystic" if it has at least 10 benign cysts on it. A woman with the syndrome will have a larger ovary and may have abnormal hormone levels - including raised levels of testosterone (the hormone that influences hair growth), oestrogen (which stimulates the growth of the womb lining), and insulin which is normally involved in extracting energy from food. Diagnosis is made by an ultrasound scan, which shows the cysts, and by blood tests to detect hormone levels.
Doctors believe that some women have a predisposition to the condition and that it may run in families. But they don't know why symptoms can start developing, although weight gain - caused by excess insulin - is one big factor.
Ironically, PCOS displays certain characteristics which suggest it evolved in the past as a means of maintaining fertility. "In times of famine, women with a tendency to obesity preserve the population by maintaining fertility, while those of normal body weight fall below the threshold body weight at which they can have periods," explains consultant gynaecologist Adam Balen.
PCOS can have very obvious symptoms aside from weight gain: increased hairiness and acne, and, for three-quarters of women, irregular or non-existent periods.
But some women appear to be outwardly unaffected. "There are a collection of signs and symptoms, and there's a big spectrum," says Balen, a consultant in reproductive medicine and surgery at Leeds General Infirmary. To make things even more confusing, it's possible to have polycystic ovaries but not the full syndrome if you fail to display any of the symptoms.
"If you look at a traditional text book, it says sufferers have to be overweight, not have periods and have unwanted hair, but the majority of women don't actually fit into that neat pigeonhole," says Balen. "In the largest study of PCOS conducted among 1,800 women, we found 60% were slim. There is an increasing awareness of the condition, but I don't think some GPs are sufficiently aware of the breadth of it."
That was certainly the experience of Olivia Bower, 28, a teacher from north London, who went to her GP after missing her periods for a year and was finally diagnosed with the syndrome. Extremely slim, and with no spots or excessive hairiness, she says: "Even my doctor didn't think I could have it because I didn't have any of the symptoms."
But for Colette Harris, 29, editor of Here's Health and author of PCOS: A Woman's Guide to Dealing with Polycystic Ovary Syndrome, diagnosis came after she displayed the whole range of symptoms. "I was washing clumps of hair from my head every week, my weight was steadily climbing and I was getting more and more painful lumpy red spots. When I started to get fine dark hairs on my upper lip, I decided my hormones were playing up and went to the doctor."
For many women - particularly those enduring the most severe symptoms - the syndrome can be a crushing blow. "There's the whole self esteem issue around your body image and fertility," says Harris. "It's so tied up to your sense of self as a woman, and when you're putting on lots of weight, and getting obvious facial and body hair and bald patches and loads of spots, you can feel you're losing your femininity."
There are also health concerns. Having PCOS makes you more prone to developing diabetes, with up to 35% of overweight PCOS sufferers showing signs by their 30s. There's also an increased chance of high blood pressure and high cholesterol, both of which can lead to heart disease; of miscarriage, should you become pregnant; of breast cancer, and of endometrial cancer since, with irregular periods, the womb lining is not shed frequently.
But the most cruel aspect can be the fear and uncertainty it provokes surrounding your ability to have a baby. "I went to my doctor two years ago after failing to conceive for a year," says Sara Tennant, a 32-year-old lawyer still trying for a baby. "I was relieved to be diagnosed and I'm being positive, but I do have some really hideous moments."
But the good news, as Jules Oliver's increasingly massive bump and Posh's weekend announcement both testify, is that having PCOS does not necessarily bar you from getting pregnant. Although Beckham apparently took advice on changing her diet and taking supplements, she would appear to be one of the lucky ones who do ovulate and, two years into trying, conceived without any medical treatment.
Jules Oliver didn't have it so lucky. She reportedly endured a "course of powerful fertility pills and antibiotics" at London's Hammersmith hospital before conceiving. This treatment would have involved a tablet called clomiphene citrate (Clomid), which induces ovulation in three-quarters of women, of whom 50-60% can expect to get pregnant after six months.
If that fails, however, daily hormone injections of a drug containing a follicle-stimulating hormone can help, with 60-70% of women who receive this getting pregnant within six months. Controversial keyhole surgery, in which ovaries are cauterised - called ovarian drilling - will also induce ovulation in 80% of women. But, if all this fails, you may have to look to even more drastic measures such as IVF.
Balen is reassuring about the likelihood of conceiving before things reach this stage. But he does suggest that reducing weight through a healthy diet and taking exercise can prove crucial in boosting the chances of conception. "Exercise can kickstart the metabolism, and keeping your weight down also reduces your risk of miscarriage and of diabetes."
Alternative medicine may also help, and Harris - who refused the conventional "treatment" of going on the pill to induce false bleeds - has managed to regulate her periods by cutting out alcohol and caffeine, eating a vegetarian diet, and taking the herbal remedy agnus castus. The move has also boosted her self-confidence. "Many women feel like their body's being taken away from them, that they're out of control in all this. But doing something about your nutrition and increasing your exercise is something you can do for yourself."
Support is also provided by the self-help group Verity (www.verity-pcos.org.uk), but, in the end, perhaps the best boost is provided by the example of Ann Pring, a 47-year-old teacher from Liverpool, who has managed to have six children, now aged between 11 and 23, despite suffering from PCOS since, her GP suspects, her teens.
Pring, who went to her GP after becoming depressed about being overweight and hairy, says: "My doctor just looked at me and said by rights I shouldn't have had the kids. I thought that was a silly thing to say. I had terrifically irregular periods but obviously just managed to get it right each time."