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When Jennifer Baumgardner, a New York City based mother-of-two had her first baby around the same time as her close friend, the other woman suggested that the two nurse each other’s infants so they could be “milk siblings.”

At first, Baumgardner balked, but eventually she came around to the idea — in fact, she ended up loving the experience. “I didn’t think there was anything gross or sexual about it,” she tells Yahoo Parenting.

The practice is called “cross nursing” and while it’s tough to find statistics on exactly how many women do it, once you start asking around, it seems that plenty of mothers have either nursed someone else’s baby or had someone nurse their own. Reasons to cross-nurse include sharing a bond with another breastfeeding friend, supplying an infant with milk if his or her mother doesn’t produce enough, and providing respite from the physical demands of nursing.

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However, due to potential health concerns, the Food and Drug Administration (FDA) discourages the practice. Cross-nursing could spread diseases such as tuberculosis, syphilis, hepatitis-associated antigens, herpes virus, and HIV, according to Diana West, the director of media relations at the breastfeeding support group La Leche League International (LLL). West adds that LLL neither encourages or discourages the practice of cross-nursing.

In fact, West herself once cross-nursed a friend’s six-week-old baby because her mother had to take a trip and didn’t want her child to experience nipple confusion by drinking from a bottle. “I didn’t mind,” West tells Yahoo Parenting.

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Yet some medical experts say cross-nursing is unnecessary. “If a woman does not produce enough breast milk to feed her baby, there are multiple options for supplementing with formula,” Dyan Hes, M.D., medical director of Gramercy Pediatrics in New York City, tells Yahoo Parenting.

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“Breast milk changes as babies age,” she adds. “The contents of one-month-old postpartum milk are not the same as milk that’s nine-months-old. A woman will not make breast milk suitable to another child’s age-appropriate requirements.”

And, as any nursing mother knows, it’s not always easy to get a newborn to latch correctly. “Babies who are cross-nursed are often confused by feeding from two different women,” Hes says. The difference in milk flow, nipple shape, and feeding position could result in the baby refusing to latch. And medication and lifestyle choices may interfere with the health of the nursing baby.

However, Lisa Baker, a mother-of-two from Georgia, chalks up such concerns to scare tactics. “We get tested for all this stuff during pregnancy, right? What’s the likelihood?” she tells Yahoo Parenting. In her group of self-described “hippy mom” friends, cross-nursing is pretty commonplace.

Baker’s first child, now six-years-old, wanted to nurse constantly and once spent 22 hours of a 24-hour period latched onto her mother. “I would have given anything for a break,” says Baker. “If she wasn’t nursing, she was screaming, That was really hard. I would just daydream about living in a commune where someone else could nurse.”

The women in Baker’s mom group also stepped in to nurse another mother’s baby when she was having trouble breastfeeding. As a result, the mother gained confidence and was soon able to feed her baby.

Paola Cruz, a mother in Massachusetts, also nursed the baby of her sister, who was engorged and unable to feed her newborn. Later, when Cruz had an abundance of milk and her sister didn’t, she pumped into bottles for her niece.

“I had plenty,” Cruz says. “I don’t think I would’ve done it with anyone else since I wouldn’t know their medical history, diet, or hygiene habits. But my milk supply was plentiful. Had I been the one in need, maybe I would feel differently.”

In 1920, my great-grandmother lost a baby. Two weeks later, her nephew was born and his own mother was unable to nurse so my great-grandmother breastfed him for a full year. The story has become lore in my family. As a mom who nursed three children and has always produced the bare minimum, it’s hard to imagine a world where I had an oversupply. But some women do. And these women, when they share, change the lives of others.

As for the claim that a mother’s breast milk is custom-made for her child, Baumgardner dismisses it. “I hear of so many women with babies who had adverse reactions to their breast milk,” she says. “If there were this perfect system where God created milk just for their baby, why would that happen?”

Baker agrees. “There’s this huge push to convince moms that they are the only ones who can do certain things. That’s a lie,” she says. That lie is what keeps us trapped, tied to our babies, miserable at times, but unable to share the burden.

Besides, once a person has nursed enough, breastfeeding (and anything related to the idea) loses taboo and becomes utilitarian. Or, as Baker puts it: “If someone else gives your baby goldfish, what’s the difference?”

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