Almost 30 years ago, on July 25, 1978, newspaper headlines (“First Test-Tube Baby! It’s a Girl!”) heralded the first successful instance of in vitro fertilization (IVF), when Lesley Brown of Bristol, England, gave birth to a five-pound, 12-ounce baby, who was named Louise.

After nearly a decade of trying to conceive and failed attempts to clear her blocked fallopian tubes, Lesley and her husband, John, as a last resort, sought out Robert Edwards and Patrick Steptoe, who had been experimenting with a stunning new technology: conception outside the human body. First, Steptoe, a surgeon and gynecologist, retrieved an egg cell from Lesley and fertilized it with John’s sperm in a petri dish. After two and a half days, an embryo was implanted in Lesley’s uterus.

For Steptoe and Edwards (a physiologist), the success had been a decade in the making: After the pair’s first successful fertilization of a human egg in a petri dish, they spent six years implanting fertilized eggs that had undergone as many as 100 cell divisions. Few took; just one resulted in pregnancy, which had to be terminated because it was ectopic. Lesley—within whom they implanted an embryo that had only eight cells—was the first to carry such a child to term. All along, Edwards and Steptoe were repeatedly denied research funds because fellow scientists were convinced that their work would produce abnormal babies.

These days, though it is the final resort—after use of follicle-stimulating drugs alone or in combination with artificial insemination—IVF accounts for more than 1% of all pregnancies. During the past 30 years, the procedure has been refined. Now stimulating drugs produce more follicles but fewer side effects, and scientists have learned how to develop the later-stage embryos that Steptoe and Edwards attempted.

Despite such improvements, some women may undergo three to five cycles of IVF (each of which costs an average $12,400) before it works. What’s more, IVF isn’t a surefire way to beat one’s biological clock; because a woman’s egg quality declines after the age of 35, so does her chance of full-term pregnancy (at 42, as low as 8%).

Age might be a moot concern for a woman if her eggs are destroyed by, say, chemotherapy. For that reason, researchers at the Massachusetts General Hospital are experimenting with freezing a woman’s eggs before she undergoes treatment; success rates are still low, in part because the egg’s genetic machinery is susceptible to damage caused by ice formations.

Frozen embryos, much hardier than eggs, are frequently used in IVF—and, in the past decade, in stem-cell research as well. As it turned out, one controversial practice spawned another.