A £179 fertility test was launched yesterday amid concerns that women may rely on it to estimate how many more years they can delay having children.

The Plan Ahead kit counts the number of eggs in a woman's ovaries compared with the levels expected for others of the same age. A blood test can predict the ovarian reserve for the next two years, information that may help women decide whether, or how long, they can delay trying to conceive.

The product is aimed at the increasing number of women delaying motherhood as they pursue their careers, believing they will still be able to conceive late in their thirties or even early forties. Fertility starts to decrease significantly after 35 and many women who have put off having children find they are unable to conceive naturally later on.

The product's launch comes after Birmingham University produced the Fertell test for couples who are having problems conceiving. It checks the woman is ovulating and contains the first over-the-counter male fertility test.

The new test was met with caution from the Family Planning Association. A spokeswoman said: "There are so many other factors involved in fertility. It also depends on your partner's fertility and your own lifestyle factors such as whether you take drugs or drink too much alcohol, and whether a couple is taking enough time out to have sex when the woman is ovulating. There are lots of issues to look at apart from the number of eggs and this test does also not check for the quality of the eggs but simply the quantity."

The Plan Ahead test, launched by Lifestyle Choices, measures three hormones in the blood - two ovarian hormones called Inhibin B and AMH, and the pituitary hormone called FSH). Combining these results gives a forecast of the number of eggs in reserve, meaning that women who may face an early menopause are given a warning that they may not want to delay conceiving.

The test was developed by Bill Ledger, professor of obstetrics and gynaecology at Sheffield University. He said: "My hope is that Plan Ahead will help many women avoid the anguish caused by the early or unexpected arrival of declining fertility and menopause.

"Inhibin B and AMH hormone levels start to fall relatively early in reproductive life, with a later fall in FSH. By combining the test on all three, we are able to offer the most accurate ovarian reserve hormone test in the world today, which will help people plan for the future by giving a predictive assessment of the number of eggs in their ovaries."

Women who buy the test receive a kit so they can have their blood taken by a professional which is then sent off to the lab to be analysed. The woman will then receive a letter explaining the results of the test, with a telephone helpline to deal with any concerns.

Clare Brown, chief executive of Infertility Network UK, said: "There is no doubt that many couples are leaving having a family until later in life and the negative effect of that decision and the ability to conceive is well documented."

Plan Ahead is expected to be made available in chemists and private clinics later in the year.