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.

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.