Image caption Louise Brown, pictured with her son, was the world's first test tube baby

Five million "test tube babies" have now been born around the world, according to research presented at a conference of fertility experts.

Delegates hailed it as a "remarkable milestone" for fertility treatments.

The first test tube baby, Louise Brown, was born in the UK in July 1978. Her mother Leslie Brown died last month.

However, delegates at the conference in Turkey warned couples not to use fertility treatment as an "insurance policy" if they delayed parenthood.

The International Committee for Monitoring Assisted Reproductive Technologies (Icmart) presented its latest data on children born to infertile parents at the European Society of Human Reproduction and Embryology conference.

It said official figures up to 2008, plus three years of estimates, put the total number of test tube babies born at five million.

Milestone

Icmart chairman Dr David Adamson said: "This technology has been highly successful in treating infertile patients. Millions of families with children have been created, thereby reducing the burden of infertility.

IVF success rates (based on figures for 2008) 33.1% for women under 35

27.2% for women aged 35-37

19.3% for women aged 38-39

12.5% for women aged 40-42 BBC Health: IVF in depth

"The technology has improved greatly over the years to increase pregnancy rates."

About 1.5 million cycles of IVF, and similar techniques, are performed every year, resulting in 350,000 babies, Icmart said.

Stuart Lavery, a consultant gynaecologist and director of IVF at Hammersmith Hospital, said: "IVF is now part of the mainstream, it is no longer something couples are ashamed of."

However, he cautioned that the great success of assisted reproduction techniques should not lull people into thinking they could wait to have children.

"The subtext is that if people delay childbirth they may view IVF as an insurance policy that they can access at any stage.

"Unfortunately the facts still suggest that IVF success rates in women as they get older are not fantastic."

Dr Allan Pacey, senior lecturer in andrology at the University of Sheffield, said: "I think it's significant that we've got to five million. It's far more socially acceptable than it has been over the last 10 or 20 years.

"One word of warning, we should make sure that couples understand that IVF isn't a guaranteed solution and if they're in a position to have their children earlier in life then they should try and do that.

"IVF really is something that should be preserved for those people who really need it."