Researchers analyzed dozens of studies about placenta consumption and now advise obstetricians to discourage their patients from eating the placenta in any form, according to the study published in the American Journal of Obstetrics and Gynecology.
"As obstetricians, it's important to tell the truth. And the truth is it's potentially harmful and no evidence it's beneficial, so therefore, don't do it," said Dr Amos Grunebaum, lead author and obstetrician.
"Over the last few years, we've had an increasing demand from patients who wanted to take their placenta home after delivery in order to eat it."
Many animals are known to consume their placenta after giving birth, but humans typically discarded the organ until recently.
The placenta's job is to transport oxygen and other crucial nutrients to promote fetal growth, as well as filter toxins that might harm the fetus.
The first mention in literature of humans eating their own placentas occurred about a century ago, Dr Grunebaum said, but the more recent fascination with the practice has been fueled by celebrity endorsements.
Human placentas have been consumed in many forms: raw, cooked, roasted, dehydrated, steamed and capsule form, or in smoothies or other drinks.
The most common preparation appears to be in capsules.
Companies offer to prepare the placenta for consumption, typically at a cost of $200 to $400.
But Dr Grunebaum's research found no evidence in clinical studies backing the health benefits claimed by proponents of placenta-eating.
And now, potential dangers of placenta consumption are becoming apparent.
In June, the CDC issued a warning about a case of a newborn developing recurrent group B Streptococcus sepsis after the mother ingested contaminated placenta capsules.
The baby's mother had been consuming placenta capsules three times a day.
While her breast milk did not exhibit group B Streptococcus, samples of her dried placenta inside the capsules did.
It was the first "solid evidence that contaminated placenta capsules can be a source of infection," Dr Grunebaum's study said.
Inadequate heating and preparation of the placenta may also be insufficient to eradicate viruses such as HIV, hepatitis or Zika.
A woman's decision about placenta-eating "should be based on scientific information, not on wishful thinking and other thoughts that are not clearly outlined," Dr Grunebaum said.
"Ethics is among the most important subjects in medicine. We need to be able to tell our patients what's right and what's wrong ... and be ready with a response based on science."
Most US states still lack clear regulations or safety guidelines addressing placenta consumption and hospitals have their own widely varying policies regarding the release of the placenta to mothers.
The researchers conducted survey on placenta consumption and found that nearly 54 percent of obstetricians and gynecologists felt uninformed about the risks and benefits of the practice, and 60 percent were unsure whether they should be in favor of it.
