The essence of the Supreme Court‘s 1973 Roe v. Wade decision, which established a woman’s right to an abortion, was to balance a pregnant woman’s constitutional right to privacy with the hypothetical rights of a fetus that at some point might be considered a person, even while inside the womb. The Court’s compromise was to confer those hypothetical rights on a fetus when it reaches the 28th week of pregnancy.
That threshold wasn’t arbitrary; it was based on the state of medical science at the time. In 1973, doctors and midwives were sometimes delivering babies prematurely at 28 weeks—but no earlier. Clinical experience established when a fetus could be considered just developed enough to live outside the womb.
In the half-century since, the science of fetal development and early birth has advanced considerably. Neonatal physicians and researchers have modified their thinking on when a fetus is and isn’t viable outside the womb, on how it makes the transition from a bundle of cells to a thinking, feeling being, on the relationship between a fetus and the health of the mother and on the many factors that determine whether a particular premature birth will be successful.
Throughout history, societies have struggled to define human life and to balance the competing interests of mother and child. Aristotle’s notion of “quickening,” when a pregnant woman can first feel movement in her womb, served to differentiate embryo and fetus in early Western laws. The Old Testament refers to “formation,” the point at which a fetus takes on human shape. When safe methods of imaging the womb, such as ultrasound, revealed in the 1950s that movement begins earlier than previously thought, the idea of viability outside the womb emerged as an important legal milestone.
For nearly five decades, abortion law has continued to revolve around fetal viability. In 1992, the Supreme Court’s Planned Parenthood v. Casey ruling updated Roe to codify that notion, explicitly setting fetal viability as the time up to which abortion rights are constitutionally protected. As a result, the scope of each Americans’ right to abortion has depended on how early in pregnancy medical science can save very premature babies—generally held in recent years to be 22 to 24 weeks of pregnancy.
Now, with a leaked draft opinion suggesting the Supreme Court is preparing to overturn Roe, it seems likely that states will be free to throw viability-based abortion rights out the window. Some red states have already begun. In 2018, Mississippi outlawed abortions after 15 weeks of pregnancy. In September the Texas “fetal heartrate bill” essentially banned abortions after the sixth week. On May 19, Oklahoma banned all abortions from fertilization on, following a similar Alabama ban in 2019.
The Mississippi and Alabama laws never took effect because courts ruled they violated Roe, as the Texas and Oklahoma bills clearly do as well. In December, the Supreme Court heard arguments on Mississippi’s challenge to those rulings, which is what the leaked document addresses. If the court lets the Mississippi law stand, then Roe will fall.
That doesn’t mean fetal viability will no longer matter to abortion access. Of course, it may not matter to the 26 states that the Guttmacher Institute labels as “certain” or “likely” to ban most abortions, including Michigan, Ohio and Utah. And it long hasn’t mattered to the six states, including New Mexico, Vermont and New Jersey, that, along with Washington, D.C., don’t limit how far along in pregnancy an abortion can be performed.
For the remaining 18 states, including California, New York, Colorado, Illinois and Virginia, state abortion law is likely to continue to protect abortion rights up to viability. Nearly half of Americans live in one of these states. That means abortion access for the majority of women in the U.S.—both those who live in these states as well as the many tens of thousands of women who end up traveling to one of them to obtain safe, legal abortions—will remain critically dependent on where medical science stands in keeping the tiniest babies alive.
As statehouses debate their stance on abortion in a post-Roe world, as seems sure to happen in coming months, many will claim science is on their side—whatever side that is—along with various other legal, moral, religious and philosophical considerations. Science, by itself, won’t answer all the moral and political questions on abortion, nor will it heal America’s divisive politics. It sheds light on some important questions and compounds uncertainty on others. Although we know more now about the viability of the fetus outside the womb than we did 50 years ago, clarity on this issue remains a murky, controversial and in many ways frustrating quest. Science has been able to pinpoint when a developing zygote begins to show signs of what we think of as humanness—the beginnings of cognition, responsiveness to mother’s voice and so forth.
A closer look at what we know now about abortion may bring some nuance to the conversation and sharpen the debate.
The Viability Question
The question of whether a particular fetus in the womb at a particular point in a pregnancy would survive if delivered is hypothetical. But science can tell us the earliest point in a pregnancy at which babies have, in fact, survived and gone home from the hospital. There’s a clear, precise answer: 21 weeks and one day, or just over halfway through a full-term pregnancy of 40 weeks. (Pregnancies are usually dated from the last day of the woman’s period, roughly two weeks before conception, because that date is easier to pin down than conception.
Only one baby in the world has actually survived birth that early on. That baby was delivered at less than 15 ounces in Alabama in July 2020. So far, at least, that successful ultra-early delivery has been considered the exception that proves the generally accepted rule, which is that 22 weeks is the threshold at which babies have a more than trivial chance of surviving. In the U.S., 17 percent of babies delivered at 22 weeks survive, says Edward Bell, a professor of pediatrics and a neonatal specialist at the University of Iowa.
That survival rate comes with a big caveat. It’s the average for all U.S. hospitals, including those that don’t even try hard to save babies born extremely prematurely. About four out of five hospitals don’t, according to Bell’s research. That’s either because administrators and clinicians balk at throwing so much effort, and investing so much of the family’s hope and emotions, in a battle that will very probably be painfully lost, or because the hospitals simply don’t have the state-of-the-art resources needed to give the baby a good shot.
“When you look at hospitals that actively treat babies delivered at 22 weeks, the survival rate in the U.S. goes to a third,” says Bell. “In Sweden and Japan more than half survive.”
The resources required to give a 22-week preemie a fighting chance are considerable. In 1973, at the time of the Roe decision, the viability threshold was held to be a clear 28 weeks, with almost no babies born earlier than that surviving. But two big breakthroughs in the 1990s would help push the threshold down to 24 weeks. One was providing steroids to pregnant mothers who are at high risk of going into premature labor, a treatment that speeds the development of most of the fetus’s organs, and especially the lungs, so that the organs are in better shape at birth. The other was giving very premature babies lung “surfactant,” a fluid that helps open up the underdeveloped tiny tubes that line the surface of the lungs, long one of the main reasons these babies didn’t survive.
Survival rates for 24-week preemies have continued to climb over the past two decades, now reaching 90 percent at some U.S. hospitals, and as many as half of babies delivered at 23 weeks are surviving there. That leaves 22 weeks as the real front lines of premature delivery.
The progress isn’t due to further big breakthroughs, but rather to many small improvements. The improvements were inspired by the discovery in the 1990s that hospitals could dramatically reduce surgical infections not by finding a new miracle drug, but by following a long checklist of details, such as keeping patients’ heads further from the operating room door, where contamination risks are higher, and providing antibiotics before surgery. In the same way, hospitals with specialized neonatal intensive-care units (NICUs) today focus on details such as ventilators to help with breathing, close monitoring of the air temperature, precise management of fluids, medications to reduce blood clots, nipping infections in the bud and monitoring brain function.
“Now 24-week-and-above babies can do pretty well,” says Dr. Michael Nelson, an obstetrician at Washington University School of Medicine in St. Louis who has just retired. “It’s really in the past two years that 22 weeks has come to be seen as the threshold of viability.”
The Limits of Viability
These efforts require maintaining teams of experts, and the cost of caring for a single very-premature baby typically runs to more than $100,000, with a typical NICU handling 20 or more babies at once. Such advanced NICUs are beyond the reach of most hospitals. The huge variation in survival rates of extreme preemies among hospitals reflects the differences in that investment. The University of Alabama at Birmingham operates a NICU with a staff of 350, while many other hospitals have no NICU at all.
Even when receiving the most advanced treatment possible, the vulnerability of a 22-week preemie is acute. The skin is thinner than paper, the lungs may be three or more months away from being able to take in air on their own and the brain, which is still forming basic structures, bleeds easily. To develop properly, a preemie needs to bond to the mother through touch, smell and hearing—but enveloped in tubes inside a small pod with tightly controlled temperature and air, that’s often impossible. “We can’t jeopardize the infant’s health or stability to allow for that bonding,” says Dr. Katherine Kosiv, a pediatric cardiologist at Yale Medical School.
The fact that exactly one preemie ever has been saved at 21 weeks doesn’t lead many experts to predict that similar feats will become commonplace. It’s hard to find any experts who think viability will be pushed down to 20 weeks in the foreseeable future, given the severe immaturity of virtually every organ and piece of tissue in a fetus that young. “There’s definitely a kind of biological barrier below about 22 weeks, and it seems to be insurmountable by current technology,” says Dr. John Wyatt, a neonatal physician and professor of ethics and perinatology at University College, London.
And that’s just speaking of survival, without taking into account the extensive disabilities and the potentially lifelong medical and family support the most premature babies often need. These can be significant even for 30-week preemies and are often overwhelming for those born after 24 weeks or less.
About nine out of 10 extreme preemies will run into serious complications, including blindness and deafness, lung and bowel problems and various types of motor impairment and brain damage. Some of these problems can be overcome with treatment and therapy, but others require extensive care for years or decades. Sixteen months after his birth, the 20-week preemie who survived still couldn’t breathe without supplemental oxygen. Since more than a tenth of all very premature babies are born with some type of heart defect, many of them will carry the problem into adulthood. An entire medical specialty—adult congenital cardiology—has arisen to care for them.
The toll that extreme prematurity takes on the early-developing brain tends to pose the most risk and present the greatest ongoing challenge to families. “It’s a tough road for those families,” says Kosiv. “Most likely the babies will require interventions through childhood.”
It’s no wonder. At 22 weeks, the brain has just barely formed the cortex—the part that confers higher thought—and the brain cells are only beginning to form the first of the 100 trillion connections they would normally make while still safe and comfortable in a quiet, dark womb. “We now have imaging techniques that show that the brain wiring process is very different for extremely premature babies,” says Wyatt.
The concerns over the likely damage done to extreme preemies by having to continue development outside the womb have led some researchers to try to develop artificial wombs and placentas—the organ that provides oxygen and nutrients to the fetus in the womb. The idea is that the fetus would be transferred straight from the mother’s womb into a small, fluid-filled tank or bag, where the fetus’s umbilical cord would be hooked up to oxygen and nutrients.
Teams at the Children’s Hospital of Philadelphia and at the Women & Infants Research Foundation in Western Australia have separately developed artificial wombs that have kept fetal lambs alive for weeks. But most experts are skeptical that artificial wombs are feasible for humans, even if some aren’t ready to completely rule them out down the road. “These are science-fiction-y advances,” says Kosiv. “But some of the things we can do now seemed outside the realm of possibility ten years ago.”
Other Challenges for Science
While the spotlight has remained on viability and outcomes, science is striving to answer other important questions about the fetus and pregnancy. Perhaps the toughest question of all is, when can a fetus think and feel? In theory, a 22-week-old fetus shouldn’t have a lot going on in terms of awareness. Up until that stage of development, the brain hasn’t formed the cortex—the outer part of the brain that confers higher thought. In fact, up until that point, the so-called “gray matter” of the brain that does most of the thinking, feeling and sensing in the cortex and other parts of the brain simply doesn’t exist. The neurons that compose gray matter are still being produced deep inside the early-fetal brain in a small cluster of cells called the germinal matrix, one for each of the brain’s two hemispheres.
During early development, newly minted neurons have been migrating outward from the germinal matrix to take their place on the outer regions of the brain. At 22 weeks, they’ve begun the process of connecting up so they can signal each other, the essential mechanism of thought. Between 22 and 40 weeks the fetus will form some 100 trillion such connections.
While a 26-week-old fetus still has a long way to go in terms of this connection-forming process, Wyatt notes, it has gone far enough in preemies born at that age to enable them to respond to their mother’s voice—especially when the voice is electronically altered to sound muffled the way it would be in the womb. In some cases, these preemies can also respond to music and the taste of their mother’s milk.
Has enough wiring taken place in a 22-week-old to confer what we think of as thought, emotions, awareness and the ability to feel pain? The immaturity of the neuronal connections at 22 weeks would suggest not, says Wyatt. He notes that in recent years scientists have been able to safely image fetal brains in the uterus with a special MRI technique called tractography, which shows these first connections in detail. They are nothing like the rich, complex networks of connections that will be forming in the coming weeks.
And yet, he adds, there is anecdotal evidence to suggest something akin to thought and feeling may be going on even at 22 weeks. “There are well-documented cases where the fetus responds to painful stimuli, even though there’s really no cortex,” he says. “It’s possible that there are deep structures in the fetal brain that may in some sense play the role of awareness up until the cortex is formed.” But this notion is purely speculation, he says. Scientists may be reluctant to conduct research into this question for fear that tentative findings will be distorted in legal and political wrangling.
Neonatal experts are also trying to make high-risk pregnancies safer. These include cases in which the mother has heart disease, high blood pressure or diabetes, which often threaten the life of the mother and unborn child. Exacerbating those risks and making them more common is the increasing average age at which women are becoming pregnant, which hit 30 this year in the U.S., up from 21 at the time of the Roe decision. Thirty may not sound old, but by age 35 a pregnancy is formally termed “geriatric” by doctors. “Thirty-five is just an arbitrary line,” notes Washington University’s Nelson. “Risks start going up by the late 20s.”
Medicine’s success has, ironically, further added to the risks of many pregnancies. Clinicians have gotten good at saving the lives of children with severe disorders that in the past wouldn’t have been survivable. Heart defects, childhood cancers, autoimmune diseases such as lupus and diabetes—children with even the toughest cases of these and other illnesses have in the past few decades been saved by breakthrough medical care and are now reaching childbearing age. Many of them have carried vulnerabilities into adulthood that leave them at severe risk during pregnancy.
“The burden on the heart goes up as much as 50 percent in pregnancy,” says Nelson. “A woman with heart disease may be OK outside of pregnancy, but pregnancy may be too much for the heart.”
That combination of age and more survivors with lifelong disorders has contributed to a climbing maternal mortality rate. According to the Centers for Disease Control and Prevention, that rate rose in the U.S. by 36 percent between 2018 and 2020. This reality leaves doctors in a difficult position when it comes to patients who are less than 22 weeks pregnant but face mortal dangers from their pregnancy, including hemorrhaging, heart attacks and stroke. High blood pressure alone can be catastrophic. “It can pose risk to every single organ,” says Nelson. But because delivering a baby before 22 weeks will almost certainly result in an unsuccessful birth, the situation becomes stark for a woman at high risk: Continuing the pregnancy to give the fetus a chance to reach viability may well lead to her death.
Research suggests there may be another, very different way to significantly affect neonatal outcomes, at least in the U.S: by addressing racial inequities in health care, and in health-related social conditions. Doing so would lead to fewer premature births, higher preemie survival rates and lower maternal mortality.
One 2020 study, published in the journal Proceedings of the National Academy of Sciences, dramatically highlights the problem and suggests ways of addressing it. Researchers at Harvard and the University of Minnesota-Twin Cities found that Black newborns die at the hospital at three times the rate at which white newborns die—but that the high Black newborn mortality rate is cut in half for Black newborns who are treated by Black doctors.
The implications for premature births, which account for most newborn mortality, is enormous. While the study didn’t identify what factors might be behind the startling differences in mortality, most experts believe there’s a big opportunity to improve outcomes for premature babies by reducing racial and cultural biases. “We know that race is baked into everything from diagnostics to the decision of whether or not to perform a Cesarean delivery,” says Dr. Tejumola Adegoke, director of equity & inclusion and an OB/GYN physician at Boston Medical Center. “That has made race a big factor in outcomes.”
One example: Doctors know that extremely premature babies do much better when the mother is given steroids ahead of the birth. But this knowledge is helpful only if doctors recognize that an expectant woman is at high risk of a very premature birth. That means they have to pay close attention to the woman’s complaints. Yet numerous studies have shown that doctors are less likely to act on the complaints of Black patients. “We know that Black patients get less pain medication than white patients even when they rate their pain at the same level,” says Dr. Adegoke. “If that happens with something as simple as pain, what happens when a pregnant Black woman says her chest hurts, she’s short of breath, she’s not feeling the baby move?”
After Serena Williams gave birth in 2017, Williams had to argue with multiple doctors before they took her self-reported symptoms seriously enough to discover she was suffering from life-threatening blood clots, says Dr. Adegoke. The challenges are only likely to be greater for Black women who aren’t celebrity athletes.
A more obvious problem is that Black expectant women are more likely than white women to end up at an under-resourced “safety-net” hospital, where premature survival rates are generally much lower—in part because such hospitals are likely to be in that majority of hospitals that don’t even try to save extremely premature babies. In addition, Black expectant women are less likely to receive good nutrition and other health advice, and even if they receive it, they’re more likely to live in a community where accessing the recommended nutrition and other prenatal care is more difficult. These factors can contribute to poor delivery outcomes, especially with premature birth. “Are women in an environment that’s safe, that’s free of lead, where she can exercise and get the nutrition she needs?” says Dr. Adegoke. “These are questions about how we structure our communities.”
Whether medicine and society will succeed in addressing these sorts of inequities, or even in taking them seriously, remains to be seen. Given the seemingly insurmountable biological difficulties of pushing the fetal viability threshold below 21 weeks, and the fact that medicine is struggling to make even small improvements in outcomes for extreme preemies at 22 weeks, fixing these disparities may be the best bet for improving viability in the future.
Meanwhile, Roe is at the brink. The 18 states that rely on viability to establish abortion limits may simply have to do their best to wrestle with the myriad complexities as they seek to balance women’s rights and health with the rights of a fetus that may, in theory at least, be ready to survive outside the womb.