The blood test measures the levels of three hormones

Business woman Joanne Morgan, 32, and partner Martin Whitaker did not plan to have children until later in life.

But a "biology clock" blood test showed her fertility levels were similar to those of a 37-year-old, so the couple began trying for a baby.

Miss Morgan has just given birth to a healthy son, Felix, one of the first babies born with the use of the test.

The �180 Plan Ahead test measures the levels of three hormones Inhibin B, AMH, which fall before menopause, and FSH which rise.

The kit, can be bought by mail order or over the internet.

Woman have a blood test taken by their GP and return the sample to the manufacturers.

The test estimates a woman's ovarian reserve, the number of healthy eggs she has left before the menopause.

Shocked by results

"I really don't think that now was the best time to start a family because I was busy, so I thought I could get the test, find I was OK leave it a couple of years and everything would be fine," said Miss Morgan.

"My ovarian reserve for my age was lower than average, when I looked at what my age should be, I was the same as a 37-year-old or a bit older, I was really shocked."

Partner Martin Whitaker said the test helped in the planning for a family.

"The test was really valuable, if you are over 30 or 35 it gives you peace of mind to plan your family," he said.