In the late spring of 2016, Erika Christensen was thirty-one weeks pregnant, and found out that the baby she was carrying would be unable to survive outside the womb. Her doctor told her that he was “incompatible with life.” Christensen and her husband wanted a child desperately—they called him Spartacus, because of how hard he seemed to be fighting—but she decided, immediately, to terminate the pregnancy: if the child was born, he would suffer, and would not live long; she wanted to minimize his suffering to whatever extent she could.

Christensen lived in New York, a state where, since 2014, an estimated twenty-five to twenty-seven per cent of pregnancies end in abortion. Abortion was legalized in New York in 1970, three years before the Supreme Court decided Roe v. Wade. Abortion was a crime in most other states; in New York, it became a crime with major exceptions. It is still regulated in the criminal code, and, Christensen learned, it is a crime in New York if an abortion is performed after a woman is twenty-four weeks pregnant, unless the mother’s life is in immediate jeopardy. Even though the baby in her womb would not be able to live outside of it, she would have to go elsewhere to have an abortion.

Politicians had been attempting for nearly a decade to pass a law called the Reproductive Health Act, which would remove abortion from New York’s criminal code and codify the protections of Roe v. Wade, which affirms a woman’s right to an abortion, with limits, in state law. The R.H.A. had been approved multiple times by the Democrat-controlled state assembly, but it had never passed the state senate, which was controlled by Republicans.

Christensen and her medical team made arrangements for her to travel to Colorado, where abortion is essentially regulated like any other medical procedure. With help from her mother, she scrounged up more than ten thousand dollars to pay for the procedure and the trip. In Boulder, a doctor named Warren Hern administered an injection that stopped her baby’s heart but prevented her from bleeding and going into labor. Afterward, while waiting for her flight, she could not help feeling as if what she’d done was shameful and illegal. She flew back to New York and had a physically excruciating stillbirth at a hospital.

A week and a half later, she e-mailed me. I was working at the Web site Jezebel, which often publishes stories about abortion law. Christensen wanted to describe what had happened to her. When we spoke on the phone, her milk was still coming in. Her baseline experience of pregnancy had been punishing to begin with, and New York law had made it much worse.

When New York first legalized abortion, in 1970, it was one of only four states where the practice was legal. Of the four, New York’s law was the most liberal, as it had no residency requirement. Between July of 1970 and January of 1973, roughly three hundred and fifty thousand out-of-state abortion patients came to New York; in the first two years after the state law passed, sixty per cent of women who had abortions in New York came from out of state. “New York used to be an oasis,” Katie Watson told me recently. Watson is a professor and bioethicist at Northwestern, a former lawyer for the A.C.L.U. of Illinois, and the author of “Scarlet A: The Ethics, Law, and Politics of Ordinary Abortion.” “It changed things nationally,” she said, of New York State. “And then it just never updated its statute.”

The vast majority of abortions take place in the first trimester. Fewer than ten per cent of abortions occur at fourteen weeks or later, and, according to the Guttmacher Institute, only slightly more than one per cent of abortions are performed at twenty-one weeks or later. Given how rare late-term abortion is, few elected officials are willing to risk the political costs of making it a cause. Late-term abortion makes many people deeply uncomfortable: at that point in a pregnancy, we are no longer talking about a lime-size fetus that hardly resembles a person.

Doctors who perform late-term abortions have wrestled with the profound difficulties of fetal personhood; they have arguably done so to a greater extent than anyone else. Several years ago, I interviewed Dr. Susan Robinson, a now-retired late-term-abortion provider in New Mexico who appeared in the documentary “After Tiller,” about the only four doctors in the U.S. who, at the time the film was made, openly performed late-term abortions. (Dr. George Tiller, who previously had been part of that group, was murdered by an anti-abortion activist, in 2009.) Robinson told me that, in her practice, she used whatever terms her patients used. “If she refers to it as her baby, I’ll refer to it as her baby,” she said. “If she’s named the baby, I’ll use the baby’s name, too.” She would ask patients, particularly those who were there because of fetal anomalies, if they wanted to hold their baby, and if they wanted footprints. She would cry with them and pray with them. “I mean, imagine being six months pregnant and finding out your baby’s missing half its brain, and you’ve got this nursery you’ve painted at home, you’re so ready—I don’t want them to go home from the procedure with absolutely nothing to remember and honor the baby and its birth,” Robinson said.

I was in my mid-twenties when I saw “After Tiller,” and it was the first time I’d really thought about late-term abortion. I was struck by Robinson’s aura of sorrowful compassion. She spent every day with an ethical question that many people abhor. I asked her how she drew her own lines—if she ever refused to perform an abortion when a woman’s fetus was healthy. The calculus was hard, she said. Sometimes the compelling factor was that the patient was eleven years old. But what if the patient were fifteen, or sixteen? “What is the ethical difference between doing an abortion at twenty-nine and thirty-two weeks?” she said she would ask herself, weighing each situation. She’d had a patient from France, she told me, who came to her at thirty-five weeks, and she had turned that woman down. “It wouldn’t be safe,” she said.

Since that interview, I’ve come to think that understanding late-term abortion is a key to understanding abortion and reproduction generally. For people who believe that abortion is a medical procedure that a woman chooses to have, or not to have, in consultation with her doctor, why would we restrict abortion in our legal codes at all? The decision to restrict abortion in the legal code is based on the idea that there are people who want to kill babies, and the law exists to prevent killing. The conviction that we should instead regulate abortion medically is rooted in the proposition that late-term abortions happen not because women and doctors want to kill babies but because circumstances conspire to make late-term abortions necessary, and that the women who are in these situations, and their doctors, are the people best suited to decide when those circumstances have arrived.