A British team has for the first time successfully used a new "test tube" fertilization technique that better predicts which of a woman's eggs will most likely result in pregnancy, a top fertility expert said on Monday.

The treatment combines currently used prenatal screening with a new computer program that can scan the eggs for flaws in chromosomes that may lead to miscarriage.

The first patient, a 41-year-old British woman who failed 13 rounds of fertility treatment, is now pregnant, the researchers said.

The ultimate goal is more pregnancies and fewer multiple births and miscarriages, added Simon Fishel, managing director of CAREfertility, the clinic that developed the technique.

"We are going to go slowly with the technology because we don't want to raise hopes," Fishel told a news conference. "The Holy Grail is to achieve one pregnancy with one embryo."

More than 3.5 million babies have been born worldwide using assisted reproductive technology since July 25, 1978, when two British doctors delivered the world's first test-tube baby, Louise Brown.

That number is growing faster because more women are waiting longer to start having children, and cheaper air travel makes it possible for even more couples to seek in-vitro fertilisation or IVF. Most treatments are in women aged between 30 and 39.

The technique involves surgically removing eggs from a woman's ovaries and combining them with sperm in the lab. Doctors then pick the best embryos - typically one or two - and implant them in the woman's uterus.

The challenge is choosing the best embryo, said Fishel, who was part of the team that delivered Brown.

Currently, doctors often use a microscope to pick the best shaped embryos, instead of checking the DNA, Fishel said.

"We can now look at all the chromosomes in an embryo in real time so we can put forward a fresh embryo after looking at its chromosomes," he said.

Fishel's team, which refined a complex technique to detect chromosomal problems, took a sample of the tiny part of an egg called the polar body that contains half the egg's chromosomes but does not take part in the fertilisation process.

They used a new computer programme to find that two of nine eggs from the woman who had failed IVF treatment 13 times were promising candidates.

The woman, who wishes to remain anonymous, is now entering her final two months of pregnancy.

"Although it is still at a very early stage, this technique may offer a new diagnostic and therapeutic hope to couples who suffer from repeated implantation failure in IVF," said Stuart Lavery, IVF director at Hammersmith Hospital in London.