Her birth marked a medical achievement that changed the lives of hundreds of thousands of childless couples.

The BBC's Linda Duffin: Louise Brown is proud to be part of a medical revolution

But as Louise celebrates her birthday, a Sunday newspaper reports that thousands of test tube children are to be given the right to seek out their biological parents.

Louise Brown came into the world with what her mother described as "the biggest yell you ever heard from a baby", just before midnight on 25 July, 1978.

It was a historic night at Oldham General Hospital in Greater Manchester.

Gynaecologist Patrick Steptoe and his partner Robert Edwards had taken nine years to perfect the technique that allowed them to remove eggs from a woman's body, fertilise them in a laboratory, and replace them in the womb.

The technique became known as in vitro fertilisation (IVF).

First of many

Born by caesarean section, Louise Brown was soon dubbed a "test tube baby" - a phrase she came to hate.

Nowadays, Louise, who works in a nursery in Bristol, says she is proud of her extraordinary background.

But she has shunned several lucrative offers from newspapers to tell her story, and is spending her birthday weekend with friends.

About 2,000 test tube children are born in the UK every year

Her 17-year-old sister Natalie, who was also born through IVF, recently became the first test tube child to become a mother.

But her daughter, Casey, was conceived naturally.

In the last 21 years, an estimated 300,000 women around the world have conceived by IVF, 29,000 of them in the UK.

IVF births now account for about 2,000 of the UK's births each year. Because many parents are terrified of failure, they often ask for two or three embryos to be implanted, meaning many IVF children are twins or triplets.

Thousands more would like to try. But IVF is expensive and is not guaranteed to work first time.

Expensive business

Each attempt costs at least �2,000 and although some health authorities will fund the first, many say they cannot justify the cost.

An inevitable consequence of Louise's birth was the development of sperm banks.

IVF can help people with various problems. For many, although the sperm and the eggs are individually healthy, something prevents the egg fertilising.

But for some couples, the problem is not the egg but the sperm, be it a low sperm count, low mobility or whatever.

In these cases, the couple may have to look elsewhere for a sperm donor.

Many donors give their sperm for financial reasons, others simply out of philanthropy.

Anonymous fathers

But most give it on the understanding their identities will never be revealed to their "offspring".

Now the Department of Health has agreed to look into ways of giving thousands of test tube children the legal right to track down their natural parents.

A Department of Health spokesman said a consultation paper paving the way for changes to the Human Fertilisation and Embryology Act is set for publication in the next few months.

Infertility campaigners warn that removing the right to anonymity will reduce the number of people prepared to donate sperm or eggs and threaten the availability of the treatment.

'Altruistic reasons'

Tim Hedgeley of the National Fertility Association, Issue, said: "This may be a victory for children, but it certainly is not for the donors.

"Their rights have to be protected too. People already give for altruistic reasons and now they are going to be hammered for it."

Mr Hedgeley, himself a sperm donor, said he would not have donated if he had been told the children born as a result would be able to find him and call him "father".

The proposals are due for publication this autumn, but it is understood they will not apply retrospectively.