Pincus began studying hormonal biology and
steroidal hormones early in his career. He was interested in the way that hormones affected mammalian reproductive systems. His first breakthrough came when he was able to produce
in vitro fertilization in rabbits in 1934. In 1936, he published his experiments' results. His experiments involving
parthenogenesis produced a rabbit that appeared on the cover of
Look magazine in 1937. To create the in-vitro rabbit offspring, 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's experiment became known as "Pincogenesis" because other scientists were unable to reproduce Pincus's results. After he was misquoted in an interview, it was believed that his experiment was the beginning of the use of in vitro fertilization by humans. In 1944, Pincus co-founded the
Worcester Foundation for Experimental Biology in
Shrewsbury, Massachusetts. He wanted to continue his research on the relationship between hormones and conditions such as (but not limited to) cancer, heart disease, and
schizophrenia. By the end of the 1960s, more than 300 international researchers came to participate in the
Worcester Foundation of Experimental Biology. Pincus remained interested in mammalian reproduction systems and began to research
infertility. In 1951,
Margaret Sanger met Pincus at a dinner hosted by Abraham Stone, the director of the
Margaret Sanger Research Bureau and medical director and vice president of the
Planned Parenthood Federation of America (PPFA), and procured a small grant from the PPFA for Pincus to begin hormonal contraceptive research. Pincus, along with
Min Chueh Chang, confirmed earlier research that
progesterone would act as an inhibitor to
ovulation. In 1952, Sanger told her friend
Katharine McCormick about Pincus and Chang's research. Frustrated by PPFA's meager interest and support, McCormick and Sanger met with Pincus in 1953 to dramatically expand the scope of the research with a 50-fold increase in funding from McCormick. Pincus was interested by Sanger's work with impoverished women with histories of many pregnancies. Sanger indirectly influenced him to create a successful contraceptive to prevent
unwanted pregnancies. In order to prove the safety of "the pill,"
human trials had to be conducted. These were initiated among infertility patients of
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
Edris Rice-Wray and
Celso-Ramón García. Some of the women experienced side effects from the trial medication
(Enovid), and Rice-Wray reported to Pincus that Enovid "gives one hundred percent protection against pregnancy [but causes] too many side reactions to be acceptable". Pincus and Rock disagreed with Rice-Wray based on their experience with patients in Massachusetts and their research found that
placebos caused similar side effects. Subsequently, trials were expanded to
Haiti,
Mexico, and
Los Angelesdespite high
attritionto accommodate rising interest. In May 1960, the
American Food and Drug Administration extended Enovid's approved indications to include contraception. ==Personal life==