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How mechanical engineering could revolutionize the study of preterm birth

Scientists are using artificial cervices and 3D models of the uterus to better understand pregnancy and childbirth.

ByKatherine J. WuNOVA NextNOVA Next
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After giving birth to her daughter Aameira (right) after just 25 weeks of pregnancy, Jasmine Zapata received a cerclage—a stitch at the base of her cervix—to bring her third child, Lillyanna, to full-term. Also pictured is Zapata's son, MJ (left). Image Credit: Courtesy of Jasmine Zapata

Jasmine Zapata was just under six months pregnant when she felt a sharp, tight pain clench in her lower abdomen.

When the discomfort didn’t pass, Zapata—then a medical student at the University of Wisconsin-Madison—phoned a triage line, where a nurse assured her she was experiencing false labor pains. Then she noticed blood trickling between her legs.

By the time she arrived at the nearest delivery room, Zapata was 10 centimeters dilated, and her amniotic sac—the fluid-filled chamber cushioning her unborn daughter—was bulging out of her cervix. Her baby, she realized, could be born any minute.

“My doctors said, ‘You’re going to meet your baby today,’” recalls Zapata, who had given birth to a healthy, full-term son, MJ, just a year and a half earlier. “When I heard that, my heart fluttered. This was my first daughter. I was so excited.” But that rush of joy quickly turned into a sinking feeling. Her due date was still 15 weeks away. It was too early, she thought. It was too soon.

Zapata was rushed into an emergency cesarean section. On the afternoon of September 10, 2010, not three hours after Zapata first felt unwell, her daughter Aameira entered the world. Before her mother even had the chance to hold her, Aameira—who weighed just 1.5 pounds—was whisked away to the neonatal intensive care unit (NICU). She would spend the first three months of her life there, hooked up to a ventilator while she battled a brain bleed, plummeting blood pressure, and a bacterial infection.

It was three weeks before Aameira was stable enough to be held. And another three before her fragile lungs grew strong enough to cry.

Now nine years old, Aameira is healthy, active, and thriving. “She does all kinds of sports, she plays the piano and sings,” says Zapata, who’s since become a pediatrician at her alma mater. She considers herself and her family lucky—because millions of women and children around the world don’t get the same ending.

Globally, preterm birth, delivery that occurs before 37 weeks gestation, is the leading cause of death in children under the age of five, affecting about 10% of infants born each year—and rates are on the rise. The babies who survive are at a higher risk of developing learning disabilities, vision and hearing problems, and chronic conditions like asthma.

But doctors still struggle to diagnose and prevent preterm birth—in part because a lot of what happens north of the vagina during those nine-ish months remains mysterious. Researchers don’t even know the true trigger of full-term labor.

“We’re still in the dark ages with obstetrics,” says Helen Feltovich, an obstetrician at Intermountain Healthcare in Utah. “There are people hurt on a daily basis by a problem we should have solved a long time ago.”

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Jasmine Zapata with her daughter, Aameira, born just 25 weeks into her mother's pregnancy in September 2010. Image Credit: Courtesy of Jasmine Zapata

Feltovich is one of several researchers now trying to harness physics and engineering to investigate issues in obstetrics—fields that traditionally have had little, if anything, to do with each other.

Like any bodily process, though, the act of growing and delivering a new human into the world is a fundamentally biomechanical phenomenon—one that requires coordination between a complex series of events, Feltovich says. Muscles contract and relax; tissues stiffen and soften; fluids gush back and forth. Understanding birth at any stage, she explains, means getting a good handle on the forces that govern it.

“That’s what we need right now,” she says. “People thinking differently about this problem.”

The last line of defense

Most of the time, preterm birth happens spontaneously: At least three weeks before her due date, a mother-to-be will feel her water break or, as Zapata did, start labor contractions. The causes—of which there are many—aren’t always clear, but many paths seem to culminate in a premature change in the cervix: a neck-like tube of tissue that comprises the lowest part of the uterus, and the last anatomical line of defense between the womb and the outside world.

The cervix should be dynamic, says mechanical engineer Kristin Myers. Normally stiff and unyielding, the tissue elasticizes during pregnancy, becoming tough but pliable, like a rubber band. Right before birth, it thins, shortens, and softens until it has the texture of ripe plum, allowing a baby to pass through. But it’s the timing of this cervical shift that can sometimes goes awry. If the cervix opens up too early, for instance, the fetus may be born before it’s had time to fully develop.

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The cervix is the lowermost part of the uterus, and helps keep the fetus in the womb throughout development, a bit like the drawstring of a bag. Having a shorter-than-average cervix can increase the risk of preterm birth. Image Credit: Sakurra, Shutterstock

Doctors call this condition “cervical insufficiency,” and Zapata’s obstetricians think it likely had something to do with Aameira’s early arrival. As in Zapata’s case, it’s often not diagnosed in time, says Michael Gallagher, an obstetrician at George Washington University. Typically, doctors will detect the problem through a combination of a patient’s medical history, physical exams, and ultrasounds, then try to reinforce the weakened cervix with a series of stitches.

When Zapata became pregnant again in 2017, the procedure—called a cerclage—brought her second daughter, Lillyana, to full term. But in many other cases, the stitches aren’t enough to hold the tissue together.

Monitoring the cervix’s evolution during pregnancy has become a focal point of Myers’ research. In her lab at Columbia University, she and her students test the tensile strength of uterine and cervical tissues, sampled from women—some pregnant, some not—who have undergone hysterectomies. Homing in on deviations from typical texture of these tissues might someday help doctors identify early harbingers of preterm birth, says Myers, who’s currently collaborating with other researchers to develop devices that can measure cervical stiffness in the clinic.

Through her collaborations with obstetricians, Myers’ team has also acquired anatomical measurements from moms-to-be. Doctors have long known that having a shorter cervix can up the risk of preterm birth, but Myers’ findings suggest other properties, like stretchiness or width, should be taken into account as well.

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Nicole Lee, a biomechanics graduate student in the lab of Kristin Myers, performing mechanical tests on a sample of mouse cervical tissue. Image Credit: Courtesy of Kristin Myers, Columbia University

Samples from humans, however, can’t do all the heavy lifting. At George Washington University, Gallagher has teamed up with fluid dynamics experts Megan Leftwich and Alexa Baumer to build synthetic models of the cervix—the perfect subjects to help test why some cerclages fail.

Baumer, who’s currently finishing her PhD, led the design and manufacture of a series of silicone-based cervices, each with a slightly different texture, to mimic the range of hardness or softness that occurs naturally in women. To ensure that her creations were on track, Baumer would make weekly visits to the hospital across the street and ask obstetrician Alexis Gimovsky to “diagnose” and stitch up the cervices. Then Baumer would head back to the lab and try to tug the faux tissue apart.

The team is still running experiments. But their preliminary results hint at an intriguing possibility: Cerclages sewn with wide, ribbon-like sutures, rather than thin stitches that resemble fishing line, might be better at holding the cervix together.

Precision pregnancy

During vaginal childbirth, babies are squeezed headfirst into a canal that must balloon in width from about 1.5 inches to 4. It’s a violent, messy beginning: The pelvic bones spread wide; tissue often tears.

Even under ideal circumstances, “childbirth is still one of the most dangerous things a woman can do with her body,” Leftwich says.

That’s in part because, from an evolutionary standpoint, mother and fetus have different sets of priorities, says Ava Mainieri, a biologist studying female reproduction at Harvard University. While it’s in the baby’s best interest to draw as many nutrients as possible from its mother to fuel its growth, the mom needs to minimize harm to herself—and conserve her resources for future children. This “push and pull” between mother and fetus, Mainieri says, makes birth the culmination of a months-long battle. It’s one of only a few medical issues that can imperil two lives at once.

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The experimental setup in the Leftwich lab to test cerclages stitched into silicone cervices. A steel insert moves through the faux cervix, applying force until the cerclage tears or breaks. Image Credit: Courtesy of Alexa Baumer, as pictured in Baumer et al. Interface Focus, 2019

At George Washington University, Leftwich and Baumer are constructing laboratory models to better understand this process. They’re starting simple: In place of a uterus, they use a latex sack. After impregnating the bag with an egg-shaped wooden baby, they measure how much force it takes to wrest the infant free.

There’s a lot missing from the setup—purposefully so, Baumer says. But it’s a way to zero in on some crucial questions, like how amniotic fluid (in this case, water or vinegar) lubricates the baby’s perilous journey out of the womb.

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Baumer is now working on upgrading the team’s uterus to one that can “contract” on its own, powered by a series of pressured air chambers. Their new setup, Leftwich explains, will help them understand the roles the fetus, amniotic fluid, and uterus each play in generating the forces required for a successful delivery. These simulations could even help physicians identify when procedures like C-sections are necessary—and, perhaps more importantly, when they’re not.

“In much of the developed world, we do obstetrics by brute force,” Leftwich says. “If anything goes wrong, we do a C-section.” Much of the time, these surgeries are life saving. But while about a third of babies in the United States (and more than 20% worldwide) are delivered this way, the World Health organization estimates that C-sections are medically imperative in just 10 to 15% of births. The rest may be putting millions of mothers and their infants in unnecessary peril with an expensive, invasive procedure that takes longer to recover from. If the mechanics of delivery become less of a black box, Leftwich says, maybe some of these cases can be averted.

“It’s really hard to study human birth, and there’s no good model system to do it,” Mainieri says. “But this gets at pregnancy and birth in humans, without using humans, and that’s phenomenal.”

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A latex uterus, suspended from an aluminum frame in the lab of Megan Leftwich at George Washington University. In some tests, this uterus is impregnated with a wooden "fetus." Image Credit: Courtesy of Alexa Baumer, as pictured in Lehn et al., Journal of Biomechanics, 2019

At Columbia, Myers is making models, too, but of a different sort: digital simulations of the uterus and cervix, built from ultrasound scans taken by her collaborators.

Her ultimate goal is to get medicine a little closer to the concept of precision pregnancy—a future in which each woman can have access to a personalized 3D computer model that captures how her unique anatomy and physiology might affect her and her child’s wellbeing. (One of her next collaborative efforts also involves Feltovich and Zapata.) Someday, Myers says, these models could even help doctors identify effective interventions when appropriate. For now, they’re already giving her team a lens into the body that biopsied tissues alone can’t offer.

“This is about hypothesis generation,” she says. “Having something visual tends to spark conversation and ideas.”

More than mechanics

Preterm birth is one of the largest global public health challenges out there—and that won’t be something with an easy fix, says Anne CC Lee, a perinatal epidemiologist at Brigham and Women’s Hospital in Boston.

Around the world, millions of women go into preterm labor that’s prompted by infection, malnutrition, stress, and other conditions that intertwine the biological and physical with the social and political. Countless socioeconomic factors can affect a mother-to-be’s trajectory, says Lee, who has spent years studying birth outcomes in lower-resourced parts of the world.

To avoid widening health disparities further, “equity needs to be in people’s minds from the beginning,” says Lina Roa, an obstetrician and public health researcher at Harvard Medical School. Mechanical models of pregnancy and birth could have far-reaching benefits on a global scale, she says. But their reach will be limited if they’re not a part of a larger effort to address inequality as a whole.

Even higher-income countries like the United States are not immune to these problems. Here, rates of preterm birth are more than 50% higher among black women than among white women—something that researchers have linked to the negative health impacts of persistent racial discrimination and stress. Black women are also three to four times as likely as white women to experience a pregnancy- or childbirth-related death.

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The Zapata family, from left to right: mother Jasmine, baby daughter Lillyanna, father Miguel, son MJ, and older daughter Aameira. Image Credit: Courtesy of Jasmine Zapata

Due in part to a long history of inequitable medical practices, a great deal of distrust still exists between people of color and the United States healthcare system, says Zapata, who is African American. Even today, she says, implicit bias among medical professionals leaves black patients undertreated compared to their white counterparts.

Much of the data that researchers are using to better understand pregnancy and childbirth—mechanically or otherwise—still comes from exams performed on white women, Leftwich says. That’s a discrepancy many scientists are trying to fix, she says, but change is slow.

Compounding the issue is the fact that reproductive sciences remain a disproportionately underfunded sector of research. “Women are 50% of the population,” Mainieri says, “but women’s health is still considered niche.”

And within the small group of researchers who blend physics and pregnancy, there’s some stigma to grapple with, Leftwich says. Baumer, her student, is known in their male-dominated department as “the cervix lady.”

“We often get [male] visitors in our lab,” Leftwich says. “They’ll ask me, ‘How did you think of this, of studying childbirth?’ I say, ‘I did it twice. I couldn’t not think of it.’”

Part of the battle, Zapata says, is raising awareness. After Aameira’s birth, Zapata decided to pursue a dual career in medicine and public health to understand the ways premature birth can be not just treated, but prevented.

Aameira is her daily reminder of just how worthy that goal is. When Zapata, the current spokesperson for the nonprofit organization March of Dimes, travels to share her experiences, her daughter often joins her. Their conversations about the circumstances of Aameira’s birth are honest and frank, Zapata says.

After having an intravenous line inserted into her forehead during her stay in the NICU, Zapata’s daughter was left with a permanent scar that provoked teasing when she first entered school. Aameira once asked her mother if the mark made her “weird.”

Zapata replied with a firm no. “Your scar makes you beautiful,” she told her daughter. “It shows you’re a warrior. It shows how much you overcame.”

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