Some 83 percent of babies in the United States start out on breast milk, but by 6 months, just 56 percent are breastfed — and at that stage, only a quarter drink breast milk exclusively, as the American Academy of Pediatrics recommends. To find out what it takes to breastfeed a baby, The New York Times followed four mothers for a day as they nursed, pumped and supplemented their milk with formula. Dr. Ma returned to work four weeks after her oldest daughter’s birth and two weeks after her second arrived. While performing long operations, she leaked breast milk under her surgical gown. Now her hours are more reasonable, and she has an office with a door that locks — but Dr. Ma still feels relentless pressure to keep up.

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