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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A mother feeds her new baby at the Yida refugee camp in South Sudan, which has the highest maternal mortality rate in the world. About 1 in 7 women in South Sudan die from causes related to pregnancy. Paula Bronstein/Getty Images hide caption

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Pakistani toddler Mohammad Musa, seen here sitting in his grandfather Muhammad Yasin's lap after a court hearing in Lahore. A court threw out charges of attempted murder against the toddler Saturday. Arif Ali/AFP/Getty Images hide caption

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We know it's not really about Mr. Stork. But we might not be up to speed on key aspects of conception. Jens Bonnke/ImageZoo/Corbis hide caption

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You tried burping. You tried bouncing. You tried swaddling. Now what? iStockphoto hide caption

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Nurse Carina Araujo gives care to a child in the neonatal intensive care unit at Maternidade Doutor Alfredo da Costa Hospital in Lisbon, Portugal, on June 6. Portugal's birthrate has dropped 14 percent since the economic crisis hit. The Washington Post/The Washington Post/Getty Images hide caption

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He's not just getting a cold. He's building his microbiome. iStockphoto.com hide caption

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Eva Hu-Stiles virtually interacts with her grandmother. iPad assist by Elise Hu-Stiles. John W. Poole/NPR hide caption

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In a study of 4,000 pregnant women, fish accounted for only 7 percent of blood mercury levels. JackF/iStockphoto.com hide caption

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