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AS WE emerged into the world as newborns, each of us lost something important: a body part that had provided us with oxygen and nutrients, removed waste products and kept pathogens at bay. What became of this crucial organ? It was probably thrown in the bin – assuming it wasn’t served up to your parent in the belief that eating it would do them good.

Never mind, you might say. After all, the body part in question – the placenta – is supposed to be a temporary organ. No one wants to go through life attached at the navel to a blob of tissue that looks like a meaty, 20-centimetre-wide mushroom. The moment the umbilical cord is cut, the placenta’s influence on our well-being is severed too.

Or so we used to think, but we were wrong. We are now learning that your placenta may have a surprisingly large hold over your health decades after you lose it. Heart disease, obesity, asthma, several forms of cancer – your long-term risk of all of these conditions might be influenced by the way your placenta grew.

This news comes too late to help anyone already born. But future generations could benefit if we can develop tools to spot unhealthy placentas during pregnancy and new therapies to treat any problems. Motivated by the potential of such tools to improve human health, researchers are now racing to develop them – and in the past 12 months, their efforts have begun to bear fruit. So, are we poised to give babies-to-be a better chance of enjoying a healthy life?

The placenta begins to develop from an embryo’s cells . As the embryo grows into a fetus, the placenta serves as its interface with the parent (see “War of the womb”). This means it brings oxygen and nutrients to the developing fetus. But it does much more, single-handedly performing all of the jobs that, after birth, . To achieve this feat, the placenta oversees the complete remodelling of the nearly 150 spiral arteries – small, coiled blood vessels in the uterus – that supply it with blood. However, the process doesn’t always go smoothly.

“The placenta is an incredibly weird and miraculous organ that we grow for this very short period of time, but there’s any number of ways it can go wrong,” says at the Montefiore Medical Center in New York City. When it does, the health of the parent or the fetus – or both – may be at risk.

Take pre-eclampsia, which each year leads to the deaths of and is also a factor in 500,000 stillbirths. Although the exact cause of pre-eclampsia is debated, it occurs when the spiral arteries remodelled by the placenta don’t transform properly. The vessels don’t widen correctly, starving the fetus of oxygen. The fetus responds by into the bloodstream of the parent. This ultimately causes blood vessels to constrict and blood pressure to spike. Unchecked, pre-eclampsia can cause damage to the parent’s brain, heart, liver and kidneys and leave the fetus at risk too.

Then there is placenta accreta, a serious condition in which a newly formed placenta doesn’t stop growing after invading the uterus. In severe cases, it pushes all the way through the wall of the uterus into adjacent organs, including the bladder or bowel. Then, when the baby is delivered “the placenta can’t unattach as it’s embedded too deeply”, says Karkowsky. “People just bleed a tremendous, life-threatening amount.”

Placenta problems

It is also thought that . This is a concerning figure given that research in the past 20 years has linked preterm births with long-term health issues in the parent. For instance, in a 2020 study, at the Icahn School of Medicine at Mount Sinai, New York, and his colleagues looked at data collected from more than 2.1 million women in Sweden who gave birth between 1973 and 2015. They found that women who delivered their babies preterm had a heightened risk of developing ischaemic heart disease many years later. For women who gave birth extremely early – 22 to 27 weeks into pregnancy – Crump’s team found that .

What might explain this heightened risk? It is possible that underlying biological or genetic factors predispose people to developing heart problems and also to delivering pregnancies preterm. A genetic explanation would fit with evidence that . However, Crump’s team pointed out an alternative: in at least some cases, the process of preterm delivery itself might trigger inflammation that raises the risk of later heart disease. In line with this idea is a 2018 study of blood samples taken from 235 women who, years later, either did or didn’t have a preterm birth. There were to indicate that the women who later had a preterm birth were predisposed to do so.

Other pregnancy complications may also have consequences for long-term health. Last year, for instance, one study suggested that in those carrying a pregnancy that affects health years later.

A fetus’s long-term health is at risk too. Evidence for this began to emerge in the late 20th century, when , a physician at the University of Southampton, UK, and his colleagues analysed the health records of 15,000 men in southern England. They found a clear relationship between a person’s weight at full-term birth – which is determined largely by the placenta – and their . More specifically, people who had been closer to 2.3 kilograms at birth were at a as adults than people who had been nearer 4 kg at birth. The finding persisted even when taking into account the social class of the men, although the researchers couldn’t work out the extent to which nutrition later in life also played a role.

Pre-birth origin of health conditions

Barker and his colleagues went on to show that people are also at greater risk of stroke, high blood pressure, type 2 diabetes, and if they had a low birth weight. In other words, they argued, the origins of many health conditions can be traced back to before birth.

The idea – which became known as the fetal origins hypothesis, or the Barker hypothesis – wasn’t without its critics. They contended that much of the evidence in its favour was and didn’t consider all of the potential confounding factors, . But over recent decades, the . Advocates include at Oregon Health & Science University, who collaborated with Barker on some studies. He says that your risk of developing cardiovascular disease – among the commonest causes of death worldwide – is influenced more by the way you grow before you are born than it is by your later lifestyle choices, although both are important. “The placenta literally influences your health for the rest of your life,” he says.

As the popularity of the hypothesis has grown, some researchers have begun responding to critics by exploring exactly how the placenta might influence fetal development and long-term health. One idea is that a poorly functioning placenta might reduce the supply of nutrients to the fetus at the moment that internal organs such as the heart and kidneys are growing. This may compromise the developments of these organs and leave them more vulnerable to health problems later in life.

In line with this, one study showed that 9-year-old children who experienced reduced fetal growth have than 9-year-olds who didn’t experience reduced fetal growth. Other studies show that infants with a low birth weight have – the structures that filter blood to make urine. In these individuals, it is believed that the remaining nephrons might experience damage from overwork and may be more likely to fail.

Experiments with animals – sheep in particular – have identified further potential developmental problems. If deprived of nutrients in the uterus, sheep have and their . A study in rats, meanwhile, shows that being starved of nutrients during gestation can in the pancreas – potentially explaining the link in humans between birth weight and type 2 diabetes.

“At some point in life, you may run out of insulin as a result of something you experienced in the womb, leading to you developing diabetes,” says at the University of Cambridge.

Life-long effects

Collectively, this body of research suggests that looking after the placenta during pregnancy may be one of the best things we can do to keep people healthy throughout their lives. But how can we achieve this?

Simply identifying who is at risk of having a problematic pregnancy would be helpful. In a 2020 study, Thornburg and his colleagues reviewed previously published data and concluded that fetal growth rates are lower if someone carrying a pregnancy experiences what the researchers call – meaning the sustained stress associated with racism, housing insecurity, food insecurity and partner violence.

Thornburg says it is important that this finding isn’t misinterpreted. “Mothers are not at fault for the size of their baby, or how the placenta grew,” he says. Instead, the results show how vital it is for society to do more to protect and support people during pregnancy.

Other researchers are looking beyond social factors. Last year, at the University of Cambridge and his colleagues analysed blood samples taken from 4200 women undergoing their first pregnancies and identified that are both associated with a . This year, Smith’s team reported that this .

Identifying those potentially at risk is only the beginning. The broader hope is that we will eventually have technology to monitor the placenta in unprecedented detail, which is a central goal of the , an ongoing research effort launched in 2015. This should allow us to spot exactly who has a poorly functioning placenta, so they can receive the care they need.

There is one thing in particular that placenta-monitoring technology should focus on, says at the University of Pennsylvania. “I think if you asked any obstetrician around the world what the holy grail is in terms of placental measurements, it would be oxygen,” he says. Last year, Schwartz and his colleagues unveiled a . In a proof-of-principle trial involving 24 women, it identified a subset of them who carried less oxygen in the placenta and who went on to develop pregnancy complications. It had previously been impossible to get this level of insight into the placenta, says Schwartz. “It was very exciting to finally be able to measure this.”

The field is moving quickly, and tools that provide even more information about the placenta are becoming available. For instance, in another study published last year, at Washington University in St. Louis, Missouri, and his colleagues used machine learning tools to analyse standard MRI scans taken from five women who went on to develop pregnancy complications. They found that the algorithm could interpret the data in such a way to . “We think our technique is very accessible to physicians,” says Wang.

The next step will be to develop techniques that allow for the treatment of placentas identified as functioning poorly. Although this is another goal of the Human Placenta Project, the research is still in its infancy, says Thornburg. But there are some promising leads. He singles out therapeutic ultrasound, which has already been used elsewhere in the human body to bring more oxygen into tissue by helping . Thornburg says it might work in the placenta too, but the idea will need further testing.

Today, there is far more awareness that the placenta has profound and long-term effects on our health. Thornburg has even described it as being at the . He is, however, realistic about where we currently stand. “We are just learning now how to define the health of the placenta,” he says. But as our understanding grows, our long-forgotten organ should finally gain the recognition it deserves.

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Jasmin Fox-Skelly is a science writer based in Cardiff, UK