When Mats Brännström first dreamed of performing uterus transplants, he envisioned helping women who were born without the organ or had to have hysterectomies. He wanted to give them a chance at birthing their own children, especially in countries like his native Sweden where surrogacy is illegal.

He auditioned the procedure in female rodents. Then he moved on to sheep and baboons. Two years ago, in a medical first, he managed to help a human womb–transplant patient deliver her own baby boy. In other patients, four more babies followed.

But his monumental feats have had an unintended effect: igniting hopes among some transwomen (those whose birth certificates read “male” but who identify as female) that they might one day carry their own children.

Cecile Unger, a specialist in female pelvic medicine at Cleveland Clinic, says several of the roughly 40 male-to-female transgender patients she saw in the past year have asked her about uterine transplants. One patient, she says, asked if she should wait to have her sex reassignment surgery until she could have a uterine transplant at the same time. (Unger’s advice was no.) Marci Bowers, a gynecological surgeon in northern California at Mills–Peninsula Medical Center, says that a handful of her male-to-female patients—“fewer than 5 percent”— ask about transplants. Boston Medical Center endocrinologist Joshua Safer says he, too, has fielded such requests among a small number of his transgender patients. With each patient, the subsequent conversations were an exercise in tamping down expectations.

To date there are no hard answers about whether such a fantastical-sounding procedure could enable a transwoman to carry a child. The operation has not been explored in animal trials, let alone in humans. Yet with six planned uterine transplant clinical trials among natal female patients across the U.S. and Europe reproductive researchers are hoping to become more comfortable with the surgery in the coming years. A string of successes could set a precedent that—along with patient interest—may crack open the door for other applications, including helping transwomen. “A lot of this work [in women] is intended to go down that road but no one is talking about that,” says Mark Sauer, a professor of obstetrics and gynecology at Columbia University.

Such a future is hard to imagine, at least in the near term. The surgery is still very experimental, even among natal women. Just over a dozen uterus transplants have been performed so far—with mixed results. One day after the first U.S. attempt, for example, the 26-year-old Cleveland Clinic patient had to have the transplanted organ removed due to complications. And only the Brännström group’s procedures have led to babies. More efforts are expected in the United States: Cleveland Clinic, Baylor University Medical Center, Brigham and Women’s Hospital, and the University of Nebraska Medical Center are all registered to perform small pilot trials with female patients who are hoping to carry their own children.

A Risky Prospect

The trouble is that uterine transplants are extremely complex and resource-intensive, requiring dozens of health personnel and careful coordination. First a uterus and its accompanying veins and arteries must be removed from a donor, either a living volunteer or a cadaver. Then the organ must be quickly implanted and must function correctly—ultimately producing menstruation in its recipient. If the patient does not have further complications, a year later a doctor may then implant an embryo created via in vitro fertilization. The resulting baby would have to be born through cesarean section—as a safety precaution to limit stress on the transplanted organ, and because the patient cannot feel labor contractions (nerves are not transplanted with the uterus). Following the transplant and throughout the pregnancy the patient has to take powerful antirejection drugs that come with the risk of problematic side effects.

The dynamic process of pregnancy also requires much more than simply having a womb to host a fetus, so the hurdles would be even greater for a transwoman. To support a fetus through pregnancy a transgender recipient would also need the right hormonal milieu and the vasculature to feed the uterus, along with a vagina. For individuals who are willing to take these extreme steps, reproductive specialists say such a breakthrough could be theoretically possible—just not easy.

Here is how it could work: First, a patient would likely need castration surgery and high doses of exogenous hormones because high levels of male sex hormones, called androgens, could threaten pregnancy. (Although hormone treatments can be powerful, patients would likely need to be castrated because the therapy might not be enough to maintain the pregnancy among patients with testes.) The patient would also need surgery to create a “neovagina” that would be connected to the transplant uterus, to shed menses and give doctors access to the uterus for follow-up care.

A small number of surgeons already have experience creating artificial vaginas and connecting them to uterine transplants. Most of Brännström’s transplant patients have been women with a condition called Rokitansky syndrome, and as a result they lack the upper part of the vagina and had to have a neovagina surgically made—typically by extending the lower vagina. Separately, surgeons that specialize in working with transwomen also often create neovaginas after castration, using skin from the penis and the scrotum.

Biological Connection

Even if the hormonal and anatomical challenges are overcome, for someone who was born producing sperm instead of eggs there would be one more hurdle: Before castration that person’s sperm must be collected and combined with a donor’s or partner’s egg to make an embryo via in vitro fertilization, and that embryo would have to be frozen until the transplant patient is ready. If the embryo is successfully implanted, the transwoman would then naturally produce the placenta required to sustain the pregnancy and begin to lactate in preparation for breast-feeding, Cleveland Clinic’s Unger says.

Experts disagree about what would be the biggest barrier to pulling off these theoretical transplants and pregnancies. Giuliano Testa, a transplant surgeon at Baylor University Medical Center who will soon be directing uterine transplant surgeries among natal women, says the hormones would likely prove the biggest obstacle. “It would really be a feat of unknown proportions,” Testa says. “I would never do this.” But he concedes the transplants are not out of the question. “At the end of the day it is two arteries and two veins that are connected with fine surgical techniques.”

Unger—who is not involved in Cleveland Clinic’s uterine transplant team trial—worries about a consistent and ample blood flow to the fetus. Bowers, who is transgender herself, says she is concerned about dangers to the fetus from a potentially unstable biological environment and unforeseen risks for the mother-to-be. “I respect reproduction and I don’t think we will ever see this in my lifetime in a transgender woman,” she says. “That’s what I tell my patients.”

Costs and ethics also pose significant barriers. Many transgender patients have already been saving for years to pay for male-to-female genital surgery— which can cost around $24,000 without insurance coverage—so a uterine transplant could be out of financial reach, Unger says. And some doctors working on the frontlines with transgender patients have expressed concerns about the ethics involved in the risks. Sauer, the gynecologist from Columbia, says that with options including surrogacy and adoption available in many locations, an experimental surgery to help patients give birth—not save their lives—seems like a huge risk. Safer, medical director for the Center of Transgender Medicine and Surgery at Boston Medical Center, agrees. “If you are going to die without a transplant, of course you take [antirejection] drugs. But this is not the case here,” he says. “This is not life and death.”

The American Society for Reproductive Medicine’s Ethics Committee is already discussing how uterine transplants could be prioritized, says Sauer, who is a member of that panel. Yet there is no discussion yet about how transgender candidates would be included in the mix. Additionally, it is unclear how demand for a uterus would be weighed by a hospital or an organization like the United Network for Organ Sharing.

Yet interest in uterine transplants is growing: Brännström, the Swedish surgeon who led the prior transplant work among women, says his inbox is now inundated with messages from less-traditional patients. “I get e-mails from all over the world on this, sometimes from gay males with one partner that would like to carry a child,” he says. Brännström does not plan to perform such procedures himself—instead he wants to focus on women who were born without a uterus or lost it due to cancer or another illness. The next natural step for those interested in assisting transgender or male patients, however, would likely be tackling this procedure among women with a rare condition called androgen insensitivity syndrome, he says. A person with AIS appears largely female, but has no uterus and is genetically male.

Amid these complex discussions there is one bright spot, the relative ease of finding the organs. Already one group has proved rich in willing donors: people who are transitioning from female to male and have also decided to have their uteruses removed. Unger says among her female-to-male patients, “one in three” have asked if they could donate the organs. Because there is no protocol set up to deal with these offers (Cleveland Clinic’s trial uses cadaver uteruses), they are currently turned down. Such potential donors may seem ideal because they are not pursuing a hysterectomy due to disease. But a major catch is the medical risk they face: A standard hysterectomy takes between a half-hour and an hour, but preparing a uterus and its associated blood vessels for transplant would keep such patients under the knife for as long as 10 or 11 hours. Clearly, the ethics of such donations would have to be studied extensively, Unger says. Like uterine transplants for transgender patients, this is all uncharted territory.