Since Hugh Fearnley-Wittingstall served placenta pate on focaccia in his 1998 series TV Dinners, the trend for consuming afterbirth has been growing.
Advocates including January Jones, the Mad Men actress, claim eating placenta can combat post-natal depression, rebalance hormones, boost milk production, reduce pain, help bonding and replenish lost nutrients after childbirth.
However a scientific review has found that none of the claims stand up to scrutiny, and suggests eating afterbirth could be dangerous because one of its roles is to absorb toxins to protect the growing foetus.
Researchers at Northwestern University in Illinois examined all the published studies about the health benefits of eating placenta - or placentophagy.
They found no evidence to support any of the health claims made by websites and blogs. More worryingly, they found no studies that examined the risk of eating placenta.
"Women really don't know what they are ingesting," said lead author Dr Cynthia Coyle.
"There are no regulations as to how the placenta is stored and prepared, and the dosing is inconsistent.
"Our sense is that women choosing placentophagy, who may otherwise be very careful about what they are putting into their bodies during pregnancy and nursing, are willing to ingest something without evidence of its benefits and, more importantly, of its potential risks to themselves and their nursing infants.
"Women really don't know what they are ingesting."
The term "placenta" originates from the Latin word for "flat cake" and is an organ within the uterus that acts as an exchange system between the mother and the baby.
The baby gets its oxygen, amino acids and vitamins and minerals from the mother through the placenta and umbilical cord. The baby gets rid of its carbon dioxide and other waste materials via the placenta into the mother's circulation. The placenta also filters out some harmful substances. Usually the placenta and the attached membranes are expelled after the baby has been born.
It is common for the umbilical cord to be clamped and the placenta to be treated like surgical waste and bagged and binned. However in some cultures, such as China, it is believed that the placenta has an emotional or spiritual affinity with the baby, and must therefore be disposed of in a suitable way such as burial. Almost all other mammals eat the placenta immediately after birth.
Study author Dr Crystal Clark, the assistant professor of behavioural sciences at Northwestern, decided to investigate the subject after some of her pregnant patients asked if eating their placentas would interfere with their antidepressant medications.
"I was surprised that it was more widespread than I anticipated," Dr Clark said.
"There are a lot of subjective reports from women who perceived benefits, but there hadn't been any systematic research."
The study appears in Archives of Women's Health.