There's no benefit to this trendy birth practice—but there are some real health risks.

Depending on how you feel about new moms eating their baby's placenta (yep, that's a thing, popularized by Kim Kardashian and other celebs), you may be grossed out, troubled, or not at all surprised by a recent review in the American Journal of Obstetrics and Gynecology cautioning against the practice.

Very few studies have been published in scientific journals on the risks and benefits of placentography—that is, the act of eating placenta, either in raw, cooked, or pill form. But those that have have found no evidence of any health benefits, the authors wrote in their paper.

There is, however, evidence of real risks. Take, for example, the recent case report from the Centers for Disease Control and Prevention, in which doctors recounted how an infant in Oregon developed a Streptococcus infection shortly after birth, but was treated with antibiotics and sent home after 11 days.

Five days later, the baby was back in the hospital—and test showed that the infection was back, too. Doctors weren't sure why, until one physician mentioned that the mother had asked to keep the placenta after delivery. The mom confirmed she'd had the afterbirth dehydrated and packaged into pills, which she'd been taking them ever since.

The placenta pills tested positive for the Streptococcus bacteria, suggesting that the mother had passed the infection back to her baby. Luckily, the baby recovered (again) after a few more weeks of antibiotics.

But back to this new review: The authors note that 53% of obstetricians and gynecologists in a recent survey said they were uninformed about risks and benefits of placentophagy—and 60% said they were "unsure whether they should be in favor of it or not."

They should not, the authors say definitively. In fact, they concluded, doctors have a responsibility to recommend against it. If that's not reason enough to discourage moms-to-be from trying the trend themselves, we've got a few more. Here's everything you need to know about the safety and science (or lack thereof) behind the placentophagy fad.

Why do people do this again?

Boosted by celebrity endorsements, placentophagy is increasingly common in the United States and other industrialized countries. Exact numbers aren’t available, but experts estimate that tens of thousands of U.S. women take part in the practice every year.

Initially popular in home-birth settings, the trend has spread to hospital births as well. In many cases, new mothers send their baby’s placentas to processing companies, which dehydrate them and make them into pills. Supporters of placentophagy claim that it can increase energy, improve mood, boost breast-milk production, and help speed postpartum recovery. They also point to the fact that nearly all mammals eat their babies’ placentas in nature.

No, they're not a great source of iron

But a study published last year in the Journal of Midwifery & Women’s Health debunked one of the main claims of placenta-eating advocates. Women need especially high amounts of iron during and immediately after pregnancy, and not getting enough of the important mineral is a common problem. Proponents of placentophagy point to the placenta's high iron content and say consuming it can help new mothers shore up their iron reserves.

To find out if eating placenta really helped boost levels in new moms, medical anthropologists at the University of Nevada Las Vegas (UNLV) recruited 23 pregnant women. After giving birth, the women took either placenta capsules or placebo pills containing dehydrated beef (considerably lower in iron than the placenta) every day for three weeks. They also had blood tests just before and soon after delivery, and at weeks 1 and 3 postpartum.

Those test results showed no statistically meaningful differences in the iron status of women in the two groups. In fact, the pills provided only 24% of the recommended daily allowance for iron among breastfeeding women.

Lead author Laura Gryder, a former UNLV graduate student, says these findings are important because some iron-deficient women may rely on placenta pills as their only non-food source of the mineral. By skipping traditional iron supplements, they are likely not getting the nutrient boost they need.

Senior coauthor Daniel Benyshek, PhD, an associate professor of anthropology at UNLV, agreed. “While there may indeed be other benefits for women who eat their placenta after birth,” he said in a press release, “the common practice of consuming the placenta in capsule form in the first few weeks after delivery does not appear to significantly improve iron levels for new mothers.”

What about those other health claims?

The UNLV researchers are now analyzing how the placenta pills affected mood, fatigue, and hormone levels in the new moms who participated in their study. Those results may shed more light on whether downing afterbirth is actually something to consider.

The new review is not the first that's looked at the evidence and found no documentable health benefits. A 2015 analysis of previous studies also found no data to support that eating placenta protected against postpartum depression, pain after childbirth, or iron deficiency, or helped with energy levels, breastfeeding, mother-child bonding, or skin elasticity.

New moms should know the risks

That's why doctors say moms should proceed with caution. Health’s medical editor, Dr. Raj, has pointed out that eating your placenta—which not only delivers nutrients to the fetus, but also filters waste away from it—could theoretically lead to an infection, especially if it’s not processed properly after delivery. Doctors think that's what happened to the mom in the recent CDC report (who then passed the infection onto her baby).

In that paper, the authors noted that the company used to package this particular placenta does ask customers about preexisting infections like hepatitis, herpes, chlamydia, and Lyme disease, but it doesn't ask about infections acquired during pregnancy or childbirth.

The company's website also states that "the placenta is cleaned, sliced, and dehydrated at 115°F–160°F (46°C–71°C), then ground and placed into about 115–200 gelatin capsules, and stored at room temperature," the authors wrote in their paper. But there are no official standards for how placentas should be handled or packaged, they added; in this case, the placenta may not have been heated to a temperature high enough to kill all the harmful bacteria.

Women who consume contaminated placenta pills can colonize the bacteria in their intestines and on their skin, the CDC researchers wrote, making it possible for them to pass the infection onto their babies. Their bottom line? "The placenta encapsulation process does not per say eradicate infectious pathogens," they wrote. "Thus, placenta capsule ingestion should be avoided."