Pincus and McCormick enlisted Harvard clinical professor of gynecology John Rock, chief of gynecology at the Free Hospital for Women and an expert in the treatment of infertility, to lead clinical research with women. At a scientific conference in 1952, Pincus and Rock, who had known each other for many years, discovered they were using similar approaches to achieve opposite goals. In 1952, Rock induced a three-month anovulatory "pseudopregnancy" state in eighty of his infertility patients with continuous gradually increasing oral doses of an estrogen (5 to 30 mg/day diethylstilbestrol) and progesterone (50 to 300 mg/day), and within the following four months 15% of the women became pregnant.