Kate Manning is the author of “My Notorious Life,” a novel about a 19th-century midwife.

Crocodile dung, weasel bone, beaver testicles: These are just three of the unlikely ingredients humans have used in attempts to prevent pregnancy over the centuries. But it was, finally, rabbit progesterone that provided the key to safe, effective birth control, and thereby hangs a gripping tale, one that Jonathan Eig tells with suspense and panache in “The Birth of the Pill.”

The story begins in 1950, with a meeting one winter night “high above Park Avenue” between “an old woman who loved sex” and a scientist once compared in the press to Frankenstein. The woman was Margaret Sanger, who had spent 40 years in a crusade to start the organization that became Planned Parenthood. The scientist was Gregory Pincus, author of controversial attempts to breed rabbits in a Petri dish. Sanger explained to Pincus her lifelong dream, an idea so outrageous as to seem magical: a cheap, simple birth-control method that would allow sex to be spontaneous — no risking mistakes in the heat of the moment. A woman should be able to use it without her sexual partner’s knowledge. It had to be safe and reversible, so that if the woman wanted to get pregnant, she could. A pill would be best. Can you do that? Sanger asked Pincus. He thought he could.

It is hard to recall today just how radical this proposition was in 1950. Sanger’s quest was to free women to have sex without the fear or possibility of pregnancy, thus allowing them to pursue education, careers, equal footing with men. The available birth control, in the form of condoms and diaphragms, had a high failure rate. Women were desperate to control the size of their families, as evidenced by the 250,000 letters Sanger received asking for help: “ ‘I am 30 years old . . . and have 11 children . . . kidney and heart disease. . . . Mrs. Sanger can you please help me. I have miss [sic] a few weeks and don’t know how to bring myself around. . . . I have cryed my self [sic] sick. . . . The doctor won’t do anything for me. . . . Doctors are men and have not had a baby so they have no pitty [sic].’– J.M.”

While this book might have benefited from more detail illustrating the hard lives of women before the advent of the pill, it does a masterful job explaining the imagination, perseverance and daring it took to ease their plight. In the 1950s, in most of the United States, dissemination of birth control or information about it was illegal because of “obscenity” laws. Violating those laws, Sanger was arrested many times in her long career, with a trial judge ruling in 1917 that women did not have “the right to copulate with a feeling of security that there will be no resulting conception.”

“The Birth of the Pill: How Four Crusaders Reinvented Sex and Launched a Revolution” by Jonathan Eig. (W. W. Norton)

Pincus, too, was a risk-taker, denied a post at Harvard for his radical experiments with in vitro fertilization. But with $2,000 from Sanger and Planned Parenthood, he set up a lab in Worcester, Mass., with two other scientists, M.C. Chang and Hudson Hoagland. They began testing female rabbits by injecting them with the hormone progesterone. Pincus found that, despite prolific mating habits, they did not get pregnant. The excitement engendered by this discovery is as thrilling to read about as Edison’s “light bulb moments” or Curie’s discovery of radium. Scientific inquiry, not profit, motivated Pincus (he declined to patent his research), but he needed more money to continue his work.

Enter Katharine McCormick. She was “fierce and lovely,” one of the first women to graduate with a degree from MIT and the heiress to a vast fortune. She had befriended Sanger, helping to open the first family-planning clinic in Brooklyn in 1916. One of the many marvelous anecdotes in this book tells how, in 1923, the daring McCormick helped to smuggle diaphragms from Europe by having 1,000 of them sewn into the hems of haute couture clothes and shipped to the United States by the trunkload. In 1952, she began funding Pincus’s research.

More than money, Pincus needed human test subjects. He was confident that women would eagerly try a new birth-control method, even a risky one. For centuries women had employed dangerous means to end unwanted pregnancies — syringed themselves with lye and turpentine, used probes, ingested potions of Spanish fly and tansy oil. The problem for Pincus would be how to stretch “the boundaries of law and ethics” to test progesterone on women. He needed the help of a reputable doctor.

John Rock was his man, head of the sterility clinic at the Free Hospital for Women in Boston. He had had some success in treating female fertility problems by giving his patients progesterone and estrogen. Though a devout Catholic, Rock listened when his patients explained the complexities of women’s lives: some scarred by botched abortions, others in ill health because of multiple pregnancies, many trying to raise more children than they could support. Scores of his patients begged him for a hysterectomy: It was the only method that would “guarantee an end to their baby-making days.” “As compassion . . . overwhelmed his compulsion to toe the Church’s line,” Rock’s religious views changed.

Pincus began progesterone trials with some of Rock’s patients. The team later recruited nurses and tested mental patients without their consent. The tests were an enormous burden: Participants endured endometrial biopsies, daily vaginal smears, temperature-monitoring and side effects such as nausea. Few women could stand the routine long enough to get reliable results. Eventually, the team turned to Edris Rice-Wray, a doctor in Puerto Rico. A “rebel,” she wanted to help the island’s impoverished mothers limit the number of children they bore (an average of 6.8 per woman). Beginning in 1956, progesterone was dispensed to women in Puerto Rico and Haiti. These trial subjects are unsung heroines here. About this ethically questionable phase of human testing, Eig writes that the scientists violated two protocols of modern medical research. They didn’t inform the patients of the purpose of the study or warn them of possible risks. “Was it dishonest?” Eig asks. “Most would say yes. But it did not violate any of the laws or medical standards of the day.” The scientists were lucky: Their drug proved safe, and it worked.

In 1960, the FDA approved the pill for use as birth control in the United States. Rock lobbied the pope for a blessing, too, certain that Catholics would agree that the pill was merely a refinement of the church-sanctioned “rhythm method” because it used the body’s natural hormones to control fertility. But in 1968, a papal encyclical dashed these hopes. Rock, for his efforts, was called “a moral rapist”; but among the 100 million women worldwide who take the pill today are many Catholics who ignore the church’s teachings, no doubt because, as a 1950s joke goes: “What do you call a woman who uses the rhythm method? Mommy.”

The story of four “brave, rebellious misfits,” “The Birth of the Pill” brims with fascinating detail, such as the forgotten fact that Prescott Bush — father and grandfather to presidents — served as treasurer for Planned Parenthood’s first fundraising campaign, in 1947. In our times, when progress on women’s reproductive health is undone and held hostage to the religious right, when legislatures and courts threaten to negate the miracles of science and human progress so dazzlingly portrayed here, Eig’s book is essential reading.

Kate Manning is the author of “My Notorious Life,” a novel about a 19th-century midwife.

THE BIRTH OF THE PILL

How Four Crusaders Reinvented Sex and Launched a Revolution

By Jonathan Eig

Norton. 388 pp. $27.95