Women will now be able to determine how many eggs they have left in their ovaries, allowing them to assess whether they can wait before trying to get pregnant or should get to work immediately.

Plan Ahead measures three hormone levels in the blood to assess the number of eggs a woman has, compared with levels expected for women at a particular age, said Sheffield, England-based Biofusion Plc, which is selling the over-the-counter kit.

The test costs $320.45, the company said yesterday.

A woman is born with all the eggs she will produce during her lifetime, the supply and quality of which decrease with age.

The test will enable “women to make more informed decisions about whether to try for a baby sooner rather than later,” the company said.

Fertility starts to drop when a woman is in her early 30s and falls sharply after the age of 35, doctors say. Lifestyle factors that can influence fertility include smoking, alcohol and drug use, sexually transmitted diseases, and being over or underweight.

“There aren’t any major fears about fertility in women under 35 years,” said Peter Bowen-Simpkins, a consultant gynecologist in Wales who is a spokesman for WellBeing of Women, a charity that funds research into reproductive health, in an interview. “But there is very serious concern that pregnancy is being delayed due to careers, mortgages, and lifestyles today.”

Plan Ahead, developed by Bill Ledger, professor of obstetrics and gynecology at the University of Sheffield, will be available in pharmacies and private clinics later in the year, Biofusion said. The company commercializes university-generated health-care intellectual property.