The worst surgical case of my residency came when we delivered my patient's baby by cesarean - her ninth cesarean birth.

The baby came out fine, but for the mother we suspected one of most feared complications in obstetrics - that her placenta had burrowed deep into the muscle of the uterus.

To get oxygen and nutrients to the fetus, the placenta needs to attach just a few millimeters deep into the uterus. We worried that hers had gone much farther and might eat through the entire thickness of the uterus, keeping it from shrinking back to its normal size after delivery and causing a massive hemorrhage.

We gave a gentle tug on the umbilical cord. Usually the placenta peels off with such gentle pulling, but hers remained stuck - an ominous sign.

The case points out a fundamental truth about surgical delivery: a first cesarean for most women leads to a cesarean with every pregnancy. And while a first section is quick, easy to perform, and rarely complicated, each repeat surgery carries greater risk.

More and more women are finding themselves on the C-section path. Almost one in three babies was delivered by cesarean in 2007, the most recent year for which data are available, an increase of more than 50 percent from a decade earlier.

At the same time, it's becoming harder for mothers to avoid repeat surgery. The number of vaginal births after a C-section fell by two-thirds, to fewer than 10 percent, over the same time period. This year, the National Institutes of Health estimated that since 1996, one-third of hospitals and one-half of doctors who offered vaginal births after a C-section no longer do so.

"There can be tremendous morbidity after three or four or five prior cesarean deliveries," said Gary Cunningham, an OB-GYN professor and former department chair at Southwestern Medical School in Dallas, who chaired the NIH panel.

"Women need to be counseled appropriately and accurately so that they can make an informed decision," Cunningham said. "But this doesn't do much good if she cannot find an obstetrician or hospital that will allow a trial of labor."

Repeat C-sections pose more risk than a first section for many reasons. One factor concerns anatomy. When a doctor performs a first cesarean, the layers of tissue look and feel very different from each other. These visual cues and textures guide the surgeon, indicating exactly where to cut.

The surgery is simple: the surgeon cuts, spreads, and pokes, layer by layer, until reaching the baby. The surgeon first opens the skin a few centimeters above the pubic bone. The fat underneath easily gives way until the connecting fascia is reached. The tough, fibrous fascia, which holds the intestines in the abdomen, is cut at the midline and opened in either direction. The beefy abdominal muscles beneath are spread.

Finally, the glossy peritoneum, the last layer of the abdomen, is entered, and only the uterus lies between the doctor and the baby. In a term patient, the maroon, swollen uterus, flanked by finger-size veins, fills almost the whole abdomen, pushing the intestines up. The surgeon moves the bladder out of the way, cuts the lower uterus open, and is met by a baby's foot, face, elbow, or behind, depending on how the baby is positioned.

The surgeon loses the advantage of good anatomy after the first section. The tissue undergoes scarring, toughens, and blends together as it heals. The variations in color and texture disappear. The intestines and bowel sometimes stick to the healing wound, putting them in harm's way the next time surgery is performed.

These changes increase the chances of an unexpected injury. "Her belly was cement," we'd say to one another during residency after a tough section.

A study from 2006 published in the journal Obstetrics and Gynecology compared C-section complications in more than 30,000 patients. Risks of requiring a large blood transfusion, incurring a bladder injury, needing to be on a ventilator, and ending up in intensive care all increased significantly with the number of sections after the first.

The study also showed greater risk for my patient's complication. Scarring on the inside of the uterus after a cesarean causes the placenta to attach abnormally in future pregnancies. During a first section, the risk of this complication was less than 1 in 400. After a sixth section, the risk ballooned to more than 1 in 15.

So we knew the risks my patient faced from her ninth cesarean and prepared the best we could. We matched extra blood, placed additional IV lines, and arranged for expert surgeons to back us up.

But with my patient's placenta stuck and bleeding, only one option remained: removing the entire uterus with the placenta still attached. Because the pregnant uterus is large, swollen, and filled with blood, a hysterectomy after a delivery is very dangerous and performed only as a last resort.

By the time we finished the surgery, blood covered the floor. Blood filled suction buckets, and saturated our sterile gowns and drapes. Blood-soaked sponges piled up in the corner.

My patient lost three times the entire blood volume of a normal person, sixteen liters in all. Only a massive transfusion kept her alive. Anesthesiologists pumped in 51 units of red blood cells and seven six-packs of platelets.

Vessels deep in her pelvis refused to stop bleeding, and instead of closing her, we packed her abdomen with surgical towels, hoping the pressure would stanch the slow, steady flow. She left the operating room and headed to the intensive-care unit with her abdomen still open.

After a reoperation the following morning and days in the ICU, she stabilized and slowly recovered.

With a first cesarean, the up-front costs - a few more days in the hospital, a longer recovery - may seem reasonable. Only in retrospect can the true costs become apparent.

Alex Friedman is a fellow in maternal-fetal medicine at the Hospital of the University of Pennsylvania. His e-mail address is alexander.friedman@gmail.com.