NEW YORK – The Nobel Prize in medicine went to a man whose work led to the first test tube baby, an achievement that helped bring 4 million infants into the world and raised challenging new questions about human reproduction.

Robert Edwards of Britain, now an 85-year-old professor emeritus at the University of Cambridge, lived to see the far-reaching ramifications of his hugely controversial early research.

"Today, Robert Edwards' vision is a reality and brings joy to infertile people all over the world," the Nobel Committee said in Stockholm. It began with the birth on July 25, 1978, of the first test-tube baby, Louise Brown, to a couple who had been trying to conceive for nine years.

With in vitro fertilization, or IVF, an egg is removed from a woman, mixed with sperm in a laboratory, allowed to divide for four or five days, then implanted in the womb to grow into a baby. Today the odds of a couple having a baby after a single cycle of IVF treatment are about 1 in 5, roughly the same odds as a fertile couple trying to have children naturally.

Edwards and research partner Patrick Steptoe, who died in 1988, faced opposition to their IVF experiments. Some religious leaders called it morally wrong. Some government officials thought it more important to limit fertility than treat infertility, and some scientists were worried about the safety of embryos.

"In retrospect, it is amazing that Edwards not only was able to respond to the continued criticism of IVF, but that he also remained so persistent and unperturbed in fulfilling his scientific vision," the Nobel Committee said.

Society still wrestles with issues that arose from his work, such as:

• Is it appropriate to obtain stem cells from embryos — embryos created through IVF? Some people object because the embryos are destroyed to get the cells.

• Should women who donate eggs be paid? The Vatican's top bioethics official, Monsignor Ignacio Carrasco de Paula, said Monday that Edwards opened "a new and important chapter in the field of human reproduction." But he also said IVF is responsible for the destruction of embryos and the creation of a "market" in donor eggs.

• Should there be an age limit on women using IVF? In 2006, a 67-year-old Spanish woman made headlines when she gave birth after using the technology to conceive twins. The uproar continued when she herself died only two years later.

Even so, Edwards' research deserves a Nobel, said bioethicist Laurie Zoloth of Northwestern University. "For millions of families, it created the possibility of a truly joyful and extraordinary event."

William Ledger, head of reproductive medicine at Sheffield University, said, "The only sadness is that Patrick Steptoe has not lived to see this day because it was always a joint team effort."

The Nobel is not given posthumously. It was not immediately clear why it took so long to honor such groundbreaking research. Initially, there was concern about the health of test-tube babies, "so it was, of course, very, very important that Louise Brown was healthy and that subsequent babies also were healthy," prize committee member Christer Hoog said.

Despite the absence of Steptoe, committee secretary Goran Hansson said Edwards "deserves a Nobel Prize on his own" because he made the fundamental discoveries that made IVF therapy possible.

A statement from Bourn Hall in Cambridge, England, the world's first IVF clinic, which was founded by the two researchers, said Edwards was too ill to give interviews.

"I spoke to his wife, and she was delighted. And she was sure he would be delighted, too," Hansson told reporters in Stockholm after announcing the $1.5 million (10 million kronor) award.

Lori B. Andrews of the Chicago-Kent College of Law says making embryos in a lab created a host of ethical issues that have never been fully resolved.

For one thing, clinics routinely fertilize more eggs than are implanted, at least at first. The resulting extra embryos can be frozen for storage, Andrews noted, but couples can change their minds about what they want to do with them.

These days, she said, a child can have up to five parents: the sperm donor, the egg donor, a surrogate mother who brings the child to term in her womb, and the couple intending to raise the child.

Some laws say the legal mother is the woman who gives birth, but nowadays "we can no longer depend on biology to determine the mother," Andrews said.

As for surrogate mothers, "I think there's ethical issues any time we mix human reproduction and cash payments," Zoloth said. "What does it mean to mix human reproduction and a buyer and a seller and a parent and a child in the same discussion?"

In Bristol, England, Louise Brown, the first IVF success, is now 32. In a statement issued by the Bourn Hall clinic, she said she and her mother are "so glad that one of the pioneers of IVF has been given the recognition he deserves." Brown gave birth in 2007 to a son who was conceived naturally.

Johanna Nannung is a Stockholm woman who has a personal reason to praise the award. Her daughter, Olivia, was born after she and her husband underwent four years of IVF treatments.

"It was incredible. Olivia is the most wonderful and fantastic thing that has ever happened to me. In my life I have always seen myself with a family and children. It's worth more than everything," she said.

The medicine award was the first of the 2010 Nobels to be announced. It will be followed by physics on Tuesday, chemistry on Wednesday, literature on Thursday, the peace prize on Friday and economics on Monday Oct. 11.

Candidates for the physics prize are hard to predict given the wide latitude of subjects encompassed by the award. But that does not stop experts from guessing, often by looking at winners of other physics honors, like Israel's Wolf Prize. Several Wolf Prize winners have later won the Nobel Prize.

This year, the Wolf physics award was shared by U.S. professor John F. Clauser, Alain Aspect of France and Anton Zeilinger of Austria for their work in quantum physics.

The most popular choices in a poll by the American Institute of Physics were Nick Holonyak, Shuji Nakamura and Robert Hall for the development of the LED laser.

Thomson Reuters, which analyzes high-impact scientific papers to make predictions, singled out U.S. researchers Charles Bennett, Lyman Page and David Spergel for discoveries derived from a NASA spacecraft on the age and composition of the universe.

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Karl Ritter reported from Stockholm. Associated Press writers Louise Nordstrom in Stockholm, Medical Writer Maria Cheng and Raphael G. Satter in London contributed to this report.