It's strange how the passing of just a few years can totally change your outlook. I spent most of my twenties making sure I did not get pregnant; now, three years into my thirties, I'm starting to fret about whether I will be able to reproduce at all.
My mother was 22 when she had me, and two more sisters followed at 18-month intervals. For her, having children was a priority; for me, it has always been a theoretical possibility at some point in future. But last year I fell in love and, at 33, I'm getting married in July. What was once the barely audible ticking of my biological clock has become a loud tolling.
My personal circumstances have changed at a time when the fertility of women in their thirties has become a very public health issue. Fertility experts are warning that unless we get a move on, we may be depriving ourselves of the chance of motherhood.
A few years ago, the stories were all about women in their sixties having babies after "miracle" fertility treatment. Now, there are warnings that we are all leaving it too late. Programmes such as The Baby Race, shown last week on Channel 4, have highlighted the problems many women are now experiencing in their quest to have a child.
Mothers are getting older; 15 per cent are over 35 when they give birth, and the average age of a woman when she has her first child is 29.4 years - seven years older than in the 1960s.
The facts are clear; in any one cycle, a couple has about a one in four chance of conceiving. After 35, the average woman's fertility drops by 50 per cent, while the risks of miscarriage and congenital abnormalities increase greatly. At birth, we have two million eggs; by 19 that has dwindled to 300,000, and by the time we reach 50 there are just 1,500 left. According to the fertility expert Dr Gillian Blackwood, half of women who delay having a family until after 35 won't be able to conceive naturally.
With fertility treatment having only a one in six chance of success, falling to less than 5 per cent for women over 40, doctors are warning that many women are in danger of finding themselves unable to have the children they weren't even sure they wanted a few years earlier. One in seven couples now has problems conceiving; according to Professor Bill Ledger of the University of Sheffield, that figure will rise to one in three by 2010, partly because of the number of people delaying parenthood beyond their twenties.
"It is unfair and unfortunate, but it is a simple question of biology that female fertility declines with age," Ledger says. "I think women have been reluctant to face up to that, but it is the truth and that message needs to go out loud and clear."
Which is why he developed the Plan Ahead test, a kit that aims to tell women how much time they may have left. The test measures the levels of three hormones in the blood; two from the ovaries - inhibin B and anti-Mullerian hormone (AMH) - and the follicle-stimulating hormone (FSH) from the pituitary gland. A combination of these is plotted on a graph to forecast the number of eggs a woman has in reserve, and whether that is average for her age. An ovarian reserve score may indicate that you should not put off motherhood for much longer.
The £179 mail-order test involves having a small sample of blood taken on the third day of menstruation. The sample is sent to a laboratory in Oxfordshire and the results posted back. Simple.
In my doctor's surgery, having blood taken for the test, I realised I had been blithely assuming that my results would be normal. But what if they weren't? Would I have to try to conceive sooner than I or my partner had envisaged?
Until a few years ago, many women railed against Daily Mail-style stories castigating us for putting careers before children. The Pill and other female contraceptives meant we could control our fertility and plan our families. As a twentysomething, I said I didn't want children; now I realised I didn't want not to have the choice. I thought of my sister, accidentally pregnant at 19 in what could be called a one-off contraceptive malfunction; when she tried for a second child last year, at the age of 31, it was several months before she conceived.
Ledger says: "It is a hard truth that most women trying to conceive at the age of 20 will get pregnant; in your late thirties it will be harder, and most women trying to conceive by the time they are 40 will not be successful. I think this long-term decline in fertility is not going to be reversed in the near future.
"One of the worries is the rising rate of chlamydia in girls between 15 and 24. They may not even start trying for children for another 10 years, but in a decade we could see all of those girls who did not know they were infected finding that they have blocked tubes and problems conceiving."
Fertility - or our lack of it - is now big business. Chemists stock a plethora of fertility kits for both men and women. Stuart Gall, the director of Lifestyle Choices, which is marketing Plan Ahead, says demand has been "huge" since it was launched two weeks ago. This year, Boots began selling the Fertell test, which measures a man's viable sperm.
Claire Brown, chief executive of the Infertility Network UK, warns that these tests only measure one aspect of fertility. "These kits can be good because they give you a sense of empowerment," she says. "You can do them in the privacy of your home and they can give you an idea of whether you may have a fertility problem. But we do have concerns that women could be lulled into a false sense of security. The most important thing to emphasise is that they deal with only one aspect of fertility; Plan Ahead will not tell you if you have blocked Fallopian tubes, for instance, and even if your results come back as normal, your partner could have a problem." Her advice? "Just don't keep putting it off. That has to be the message, loud and clear."
I got my test results back and opened the envelope with a surprising amount of trepidation. They were normal. I have an average number of eggs left for a woman of my age, but I was also advised to start trying for a child sooner rather than later, as that all-important 35-years-old deadline gets closer.
Am I reassured? To some extent. But I am now all too aware that time is running out. As Professor Ledger tells me: "For women like you, it can be a wake-up call. It may not be welcome, but it's the truth."
Plan Ahead is available by mail order from Lifestyle Choices (0114-275 5723; www.life-style-choices.com), and costs £179; Fertell is available at Boots, and costs £79.99. For more information, go to www.infertilitynetworkuk.com
How women - and men - can improve the odds
* Get tested: the sexually transmitted infection chlamydia is a leading cause of infertility and often has no symptoms. Smear tests and regular gynaecological examinations can also help to make sure that there are no problems.
* Stay trim: obesity can severely affect a woman's fertility, although being too thin can mean that your body may not be able to produce enough oestrogen for conception.
* Take zinc: men with low levels of zinc have been shown to have reduced sperm counts.
* Stop smoking: tobacco can affect both male and female fertility. One study found that smokers take nine months longer to conceive than non-smokers.
* Cut out coffee: some researchers believe that even a single cup of coffee a day can halve your chances of becoming pregnant.
* Stay calm: stress can adversely affect hormone levels in women and decrease the motility (movement) of sperm.
* Stop drinking: quite apart from making bedroom performance more difficult, alcohol is toxic to sperm and can reduce a man's fertility.
* Avoid waterbeds: a 2004 study found that waterbeds and electric blankets can raise the temperature of the testicles and reduce the quality of sperm.
* Keep a diary: your chances of becoming pregnant are greatest at certain times of the month. New kits are available to help you plot your optimum times of conception.
* Try alternatives: traditional Chinese medicine, acupuncture and herbal treatments may help, although one study has shown that some herbal remedies, such as St John's Wort, can in fact reduce fertility.Reuse content