The number of women buying, selling and sharing breast milk is growing rapidly. But it can be a risky purchase, scientists say, because a mom can't tell by looking at the milk whether it's safe and nutritious for her baby. iStockphoto hide caption

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Brazilian mothers participate in a demonstration in 2011 for the right to breastfeed in public, in Sao Paulo, Brazil. Eduardo Anizelli/STF/LatinContent/Getty Images hide caption

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A Mexico City breast-feeding campaigned used posters featuring topless celebrities. At least "La Barbie," a female boxer (shown here), had her boxing gloves on. Via Latin Times hide caption

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Madison Fitzgerald, 20, holds her baby, Jake, in the neonatal intensive care unit at Texas Children's Hospital in Houston. Jake, who was born 16 weeks too early, receives donor breast milk every three hours by mouth. Carrie Feibel/KUHF hide caption

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That's how it's supposed to work. But for most new moms, breast-feeding doesn't come easily, a study finds. hide caption

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This model of a molar shows color-coded barium banding patterns that reveal weaning age. Ian Harrowell, Christine Austin, Manish Arora/Harvard School of Public Health hide caption

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Some insurers prefer to pay for manual breast pumps, but some working moms prefer more expensive, electric models. hide caption

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Ashley Beecher, 29, and her daughters Annie (on lap) and Charlie. After feeding Annie, Beecher donates her extra supply to the human milk bank at Texas Children's Hospital. KUHF hide caption

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A nurse burps a baby after he's been fed, circa 1955. Doctors say that for babies with extreme reflux, off-label use of heartburn drugs can sometimes help. But frequently changes to the mother's diet can be a simpler fix. George Heyer/Three Lions/Getty Images hide caption

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