In 1915, when Adolf suddenly died, teachers at the Park School in Baltimore recognized the academic aptitudes of his twin sons and recommended that they attend Johns Hopkins University rather than begin business careers. Under the influence of the science faculty at Johns Hopkins, both Alan and Manfred Guttmacher shifted their interests from history and English to medicine. After obtaining their B. A. 's in 1919, they entered the university's famed medical school, where they were much impressed by the anatomist George Corner, a key figure in elaborating the operations of hormones.
Guttmacher's first professional paper, coauthored with his brother in 1921, was on the graafian follicle of the sow, but after receiving his M. D. 's in 1923, he worked with Corner as assistant in anatomy at Johns Hopkins (1923-1924) and at the University of Rochester (1924-1925). His marriage to Leonore Gidding on July 22, 1925, led him to turn from the relative penury of a research assistant to the practice of obstetrics in Baltimore; he nevertheless continued his academic career as a member of the medical faculty at Johns Hopkins, where he rose to associate professor before leaving to become chief of obstetrics and gynecology at New York's Mount Sinai Medical School in 1952. He retained this post until 1962. Guttmacher regarded teaching as his primary vocation and was very interested in popularizing developments in reproductive science. His first book, Life in the Making (1933), predicted revolutionary advances in the management of human reproduction, and it was followed by well-received manuals for general readers, including Into This Universe (1937), Pregnancy and Birth (1957), Babies by Choice or Chance (1959), Complete Book of Birth Control (1961), Planning Your Family (1964), Complications of Pregnancy (1965), Birth Control and Love (1969), and Understanding Sex (1970). Guttmacher was deeply affected by the deaths from septic-induced abortions that he witnessed in the wards of the Johns Hopkins Hospital, and he resented, in particular, the refusal of his mentor in obstetrics, J. Whitridge Williams, to allow him to perform an abortion for a thirteen-year-old incest victim. Appalled by the high fertility and morbidity of indigent women, who were unable to gain access to contraception and abortion, both of which were available to the wealthy, Guttmacher became an outspoken critic of what he regarded as medical hypocrisy in these matters and an advocate of the "democratization" of birth control. In the early 1960's both the Population Council and the Planned Parenthood Federation of America recruited Guttmacher for executive positions. As a member of the Population Council's medical advisory committee, he was responsible primarily for the decision to organize an international conference that revived interest in intrauterine contraceptive devices and set the stage for the council's investment of millions of dollars in the clinical testing and distribution of this technology. The Population Council was dominated by social scientists and the fact that Guttmacher was a medical doctor limited his stature within the organization; he accepted the presidency of the Planned Parenthood Federation of America in 1962. When concern about the possible side effects of the anovulant pill mounted following the discovery that the steroid tranquilizer thalidomide caused birth defects, Guttmacher aggressively defended the safety of the pill and was one of the key figures in the successful effort to maintain U. S. Food and Drug Administration approval for oral contraceptives. As president of Planned Parenthood, Guttmacher enjoyed enormous success in increasing both private support for the organization and public funding for contraceptive services. Both the staff and budget of Planned Parenthood tripled under his tenure, and his testimony before the U. S. House of Representatives Ways and Means Committee in 1967 contributed to Social Security amendments requiring that 6 percent of appropriated funds for maternal and child health services be available for family planning. Guttmacher played a similarly important role in the campaign to liberalize the laws restricting the practice of abortion. While he was at Johns Hopkins, he expressed his concern that the unilateral power of the chief of the obstetrical department to approve all abortions resulted in unacceptably arbitrary decisions. When Guttmacher became chief of obstetrics at Baltimore's Sinai Hospital in 1942, he established a committee of five drawn from relevant medical departments to review applications for abortion, and this system became standard practice in leading U. S. hospitals. After his 1952 move to New York, Guttmacher continued his efforts to rationalize the institutional circumstances surrounding abortion by supporting an American Law Institute model penal code and as a member of Governor Nelson Rockefeller's 1968 commission on abortion law reform. Several states had liberalized their laws by 1968, but Guttmacher was deeply concerned by the fact that simply making it easier to qualify medically for permission to obtain an abortion actually increased the level of discrimination against the poor. In 1969, he reluctantly concluded that the removal of abortion from the penal codes was the only fair remedy to unequal access, and he became one of the more prominent medical advocates of "abortion on demand. " In 1970 the New York state legislature passed such a law, and the U. S. Supreme Court established a similar national standard in its 1973 Roe v. Wade decision. By the time Guttmacher died of leukemia in New York City, he was convinced that changes in the law had saved lives, minimized socioeconomic discrimination, and reduced the incidence of illegal abortion. A tall and imposing figure in the hospital and on the popular lecture circuit, Guttmacher enjoyed the apparent paradox that as one of the country's most prominent obstetricians he was also an aggressive champion of birth control.
President of the Planned Parenthood Federation of America (1962), member of the Association for Voluntary Sterilization
Guttmacher married Leonore Gidding on July 22, 1925. They had 3 daughters.