At 5 A.M. on a cool Boston morning not long ago, Elizabeth Rourke—thick black-brown hair, pale Irish skin, and forty-one weeks pregnant—reached over and woke her husband, Chris.

“I’m having contractions,” she said.

“Are you sure?” he asked.

“I’m sure.”

She was a week past her due date, and the pain was deep and viselike, nothing like the occasional spasms she’d been feeling. It seemed to come out of her lower back and wrap around and seize her whole abdomen. The first spasm woke her out of a sound sleep. Then came a second. And a third.

She was carrying their first child. So far, the pregnancy had gone well, aside from the exhaustion and nausea of the first trimester, when all she felt like doing was lying on the couch watching “Law & Order” reruns (“I can’t look at Sam Waterston anymore without feeling kind of ill,” she says). An internist who had just finished her residency, she had landed a job at Massachusetts General Hospital a few months before and had managed to work until this day. Rourke and her husband sat up in bed, timing the contractions by the clock on the bedside table. They were seven minutes apart, and they stayed that way for a while.

Rourke called her obstetrician’s office at eight-thirty in the morning, when the phones were turned on, but she knew what the people there were going to say: Don’t come to the hospital until the contractions are five minutes apart and last at least a minute. “You take the childbirth class, and they drill it into you a million times,” she says. “The whole point of childbirth classes, as far as I could tell, is to make sure you keep your butt out of the hospital until you’re really in labor.”

The nurse asked if the contractions were five minutes apart and lasted more than a minute. No. Had she broken her water? No. Well, she had a “good start.” But she should wait to come in.

During her medical training, Rourke had seen about fifty births and had delivered four babies herself. The last one she had seen was in a hospital parking lot.

“The father had called, saying, ‘We’re delivering! We’re coming to the hospital, and she’s delivering!’ ” Rourke says. “So we were in the E.R. and we went running. It was freezing cold. The car came screeching up to the hospital. The door went flying open. And, sure enough, there the mom was. We could see the baby’s head. The resident running next to me got there a second before I did, and he puts his arms down, and the baby went—phhhoom—straight into his arms in the middle of the parking lot. It was freezing cold outside, and I’ll never forget the steam pouring off the baby. It’s blue and crying and the steam was pouring off of it. Then we put this tiny little baby on this enormous stretcher and raced it back into the hospital.”

Rourke didn’t want to deliver in a parking lot. She wanted a nice, normal vaginal delivery. She didn’t even want an epidural. “I didn’t want to be confined to bed,” she says. “I didn’t want to be dead from the waist down. I didn’t want a urinary catheter to have to be put in. Everything about the epidural was totally unappealing to me.” She was not afraid of the pain. Having seen how too many deliveries had gone, she was mainly afraid of losing her ability to control what was done to her.

She had considered hiring a doula—a birthing coach—to stay with her through delivery. There are studies showing that having a doula can lower the likelihood that a mother will end up with a Cesarean section or an epidural. The more she looked into it, however, the more worried she became about being paired with someone annoying. She thought about delivering with a midwife. But, as a doctor, she felt that she would actually have more control working with another doctor.

By midday, her contractions hadn’t really speeded up; they were still coming every seven minutes, maybe every six at most. She was finding it increasingly difficult to get comfortable. “The way it felt best was, strangely enough, to be on all fours,” she recalls. So she just hung around the house like that—on all fours during the contractions, her husband close by, both of them nervous and giddy about their baby being on the way.

Finally, at four-thirty in the afternoon, the contractions began coming five minutes apart, and they set off in their Jetta, with the infant car seat installed in the back. When they reached the hospital admissions desk, Rourke was ready. The baby was on the way, and she was eager to bring it into the world as nature had intended.

“I wanted no intervention, no doctors, no drugs,” she says. “I didn’t want any of that stuff. In a perfect world, I wanted to have my baby in a forest bower attended by fairy sprites.”

Human birth is an astonishing natural phenomenon. Carol Burnett once told Bill Cosby how he could understand what the experience was like. “Take your bottom lip,” she said, “pull it as far away from your face as you can, and now pull it over your head.” The process is a solution to an evolutionary problem: how a mammal can walk upright, which requires a small, fixed, bony pelvis, and also possess a large brain, which entails a baby whose head is too big to fit through that small pelvis. Part of the solution is that, in a sense, all human mothers give birth prematurely. Other mammals are born mature enough to walk and seek food within hours; our newborns are small and helpless for months. Even so, human birth is a feat involving an intricate sequence of events.

First, a mother’s pelvis enlarges. Starting in the first trimester, maternal hormones allow the joints holding the four bones of the pelvis together to stretch and loosen. Almost an inch of space is added. Pregnant women sometimes feel the different parts of their pelvis moving when they walk.

Then, when it’s time for delivery, the uterus changes. During gestation, it’s a snug, rounded, hermetically sealed pouch; during labor it takes on the shape of a funnel. And each contraction pushes the baby’s head down through that funnel, into the pelvis. This happens even in paraplegic women; the mother does not have to do anything.

Meanwhile, the cervix—which is, through pregnancy, a rigid, inch-thick cylinder of muscle and connective tissue capping the end of the funnel—softens and relaxes. Pressure from the baby’s head gradually stretches the tissue until it is paper-thin—a process known as “effacement.” A small circular opening appears, and each contraction widens it, like a tight shirt being pulled over a child’s head. Until the contractions pull the cervix open about four inches, or ten centimetres—the diameter of the child’s head—the child cannot get out. So the state of the cervix determines when birth will occur. At two or three centimetres of dilation, a mother is still in “early” labor. Delivery is many hours away. At between four and seven centimetres, the contractions grow stronger, and “active” labor has begun. At some point, the amniotic sac breaks under the pressure, and the clear fluid surrounding the fetus gushes out. Contractile force increases further.

At between seven and ten centimetres of cervical dilation, the “transition phase,” contractions reach their greatest intensity. The contractions press the baby’s head into the vagina and the narrowest part of the pelvis’s bony ring. The pelvis is usually wider from side to side than front to back, so it’s best if the baby emerges with the temples lined up side to side with the mother’s pelvis. The top of the head comes into view. The mother has a mounting urge to push. The head comes out, then the shoulders, and suddenly a breathing, wailing child is born. The umbilical cord is cut. The placenta separates from the uterine lining, and, with a slight tug on the cord and a push from the mother, it is extruded. The uterus spontaneously contracts into a clenched ball of muscle, closing off its bleeding sinuses. Typically, the mother’s breasts immediately let down colostrum, the first milk, and the newborn can latch on to feed.

That’s if all goes well. At almost any step, though, the process can go wrong. For thousands of years, childbirth was the most common cause of death for young women and infants. There’s the risk of hemorrhage. The placenta can tear, or separate, or a portion may remain stuck in the uterus after delivery and then bleed torrentially. Or the uterus may not contract after delivery, so that the raw surfaces and sinuses keep bleeding until the mother dies of blood loss. Sometimes the uterus ruptures during labor.

Infection can set in. Once the water breaks, the chances that bacteria will get into the uterus rise with each passing hour. During the nineteenth century, people started to realize that doctors often spread bacteria, because they examined more infected patients than midwives did and failed to wash their contaminated hands. Bacteria routinely invaded and killed the fetus and, often, the mother with it. Puerperal fever was the leading cause of maternal death in the era before antibiotics. Even today, if a mother doesn’t deliver within twenty-four hours after her water breaks, she has a forty-per-cent chance of becoming infected.

The most basic problem is “obstruction of labor”—not being able to get the baby out. The baby may be too big, especially when pregnancy continues beyond the fortieth week. The mother’s pelvis may be too small, as was frequently the case when lack of vitamin D and calcium made rickets common. The baby might arrive at the birth canal sideways, with nothing but an arm sticking out. It could be a breech, coming butt first and getting stuck with its legs up on its chest. It could be a footling breech, coming feet first, but then getting wedged at the chest with the arms above the head. It could come out head first but get stuck because the head is turned the wrong way. Sometimes the head makes it out, but the shoulders get stuck behind the pubic bone of the mother’s pelvis.