Bernard N. Nathanson, the son of an obstetrician-gynecologist, was born on July 31, 1926, in Manhattan and grew up on the Upper West Side. He earned a bachelor’s degree from Cornell and a medical degree from McGill University in 1949. After serving as the chief of obstetrics and gynecology for the Northeast Air Command of the Air Force, he established a successful practice in Manhattan. While interning at Woman’s Hospital in Manhattan, he observed the effects of illegal abortions on the mostly poor black and Hispanic women who came under his care, and he soon became convinced that the laws prohibiting abortion must be changed. In 1967, he met Lawrence Lader, a crusading journalist and the author of “Abortion,” and soon became caught up in Mr. Lader’s plans to organize a movement to agitate for the repeal of laws prohibiting abortions. Dr. Nathanson earned a degree in bioethics from Vanderbilt University in 1996 and that year was baptized as a Roman Catholic — he described himself up to that time as a Jewish atheist — in a private ceremony at St. Patrick’s Cathedral by Cardinal John J. O’Connor, the archbishop of New York. An obstetrician-gynecologist practicing in Manhattan, helped found the National Association for the Repeal of Abortion Laws (now NARAL Pro-Choice America) in 1969 and served as its medical adviser. After abortion was legalized in New York in 1970, he became the director of the Center for Reproductive and Sexual Health. He did his last procedure in late 1978 or early 1979 on a longtime patient suffering from cancer and soon embarked on a new career lecturing and writing against abortion. “The Silent Scream,” a 28-minute film produced by Crusade for Life, was released in early 1985. In it, Dr. Nathanson described the stages of fetal development and offered commentary as a sonogram showed, in graphic detail, the abortion of a 12-week-old fetus by the suction method. His first three marriages ended in divorce. In addition to his fourth wife, Christine, he is survived by a son, Joseph, of New Jersey.