At an early age, Anna died of tuberculosis, the cause of which was attributed to her multiple pregnancies. The premature death of her mother gave Margaret the incentive to become a nurse and start helping pregnant women. With the aid and self-sacrifice of her sisters, Mary and Nan, Margaret was able to attend Claverack College and Hudson River Institute. She then entered a nursing program at White Plains Hospital. .
While working as nurse at White Plains Hospital, she witnessed the fear and turmoil a newborn baby created in large, extremely poor families. "Most of the mothers were not ecstatic with joy at giving birth and new babies were not greeted with rapture." Margaret realized that something was greatly wrong.
Following her marriage to a young architect, William Sanger, she became pregnant with her first son, Stuart and developed tuberculosis soon after. The new family then moved to a suburb outside of New York, where she regained her health and gave birth to her second son, Grant and three years later her daughter, Peggy. She was bored and unhappy with her living and social situation in the suburbs, so the family moved back to New York. There she and her husband joined the local Socialist party, Labour Five.
Although Margaret was an active member in Labour Five, continually recruiting new members, and at the same time raising a young family, she did not feel it was enough to justify her existence. Consequently, her mother-in-law moved in with them to watch the children, so Margaret could go back to work. .
Working as an obstetrician, Margaret was called to overcrowded tenements, "where women had neither the food not the money to support the baby she was delivering." She witnessed "good" mothers bleeding to death from botched abortions and women who could never pull themselves from the depths of poverty because of their fragile health and burdens of their ever-growing families.