Gregory Goodwin Pincus (April 9, 1903 – August 22, 1967) was an American biologist and researcher who co-invented the combined oral contraceptive pill. Dr. Pincus began studying hormonal biology and steroidal hormones early in his career. He was interested in the way that hormones affected mammals' reproductive systems. His first breakthrough came early, when he was able to produce in vitro fertilization in rabbits in 1934. In 1936, he published his discoveries after his experiments. His experiments involving parthenogenesis produced a rabbit that appeared on the cover of Look magazine in 1937. To create the in vitro rabbit baby, Pincus removed the ovum from the mother rabbit and placed it in a solution mixture of saline and estrone. Afterwards, he placed the "fertilized" ovum back into the rabbit. Pincus' experiment became known as "Pincogenesis" because other scientists were unable to attain the same results when conducting the experiment. After he was misquoted in an interview, it was believed that his experiment was the beginning of the use of in vitro for humans. In order to prove the safety of "the pill," human trials had to be conducted. These were initiated on infertility patients of Dr. John Rock in Brookline, Massachusetts using progesterone in 1953 and then three different progestins in 1954. Puerto Rico was selected as a trial site in 1955, in part because there was an existing network of 67 birth control clinics serving low-income women on the island. Trials began there in 1956 and were supervised by Dr. Edris Rice-Wray and Celso-Ramón García.

Some of the women experienced side effects from "the pill" (Enovid) and Edris Rice-Wray wrote Pincus and reported that Enovid "gives one hundred percent protection against pregnancy [but causes] too many side reactions to be acceptable". Pincus and Rock disagreed based on their experience with patients in Massachusetts and conducted research showing that placebos caused similar side effects. The trials went on and were expanded to Haiti, Mexico and Los Angeles despite high attrition rates, due to the large number of women eager to try this form of contraception.

In May 1960, the FDA extended Enovid's approved indications to include contraception.