Nearly 1.2 million C-sections were performed in 2004, accounting for 29.1 percent of all births that year, the National Center for Health Statistics reported. That is up from 27.5 percent in 2003 and 20.7 in 1996.
The increase is attributed to fears of malpractice lawsuits if a vaginal delivery goes wrong, the preferences of mothers and physicians, and the risks of attempting vaginal births after Caesareans.
The C-section rate increased for all births, even those that involved healthy, first-time pregnancies with a full-term, single child. In 2000, the government announced a national public health goal of reducing the C-section rate for such births to 15 percent by 2010, but the actual rate now is about 24 percent and rising.
The government also reported that more than a half-million infants were born preterm — at less than 37 weeks' gestation — in 2004, which is another record. And the proportion of infants with a low birth weight rose to 8.1 percent in 2004, from 7.9 percent the year before.
Increases in multiple-fetus pregnancies and in pre-term C-sections seem to help explain the preterm and low birth weight numbers, said Joyce Martin, an epidemiologist who co-wrote the report.
A C-section is major surgery: A doctor cuts open a women's abdomen to retrieve the baby. The risks include infection and, in rare cases, death, and recovery time is longer than with a vaginal delivery. Doctors often perform a Caesarean when the fetus lacks oxygen or is in some other kind of life-threatening distress.
For decades, C-sections were done in only a small fraction of births. In 1970, the national rate was 5 percent. Then it rose, surpassing 20 percent by the mid-1980s.
Experts say many factors drove the rate: Mothers increasingly preferred the convenience of C-sections, which could be scheduled. Technological innovations let doctors better see problems before birth.
The trend temporarily reversed in the early 1990s, partly because HMOs pressured doctors to curtail unnecessary procedures. But by the late 1990s, health insurers had cut back their C-section control efforts.
Also, doctors became worried by studies that showed that women who deliver vaginally after having a C-section earlier suffer a ruptured uterus — a potentially lethal complication for both mother and child — in about 1 percent of such cases.
Some hospitals have banned vaginal deliveries after C-section, or VBAC, said Tonya Jamois, president of the International Cesarean Awareness Network, an advocacy organization.
"Women are struggling to avoid unnecessary surgery, but the medical system has abandoned them. For many, they have to submit to major surgery in order to get medical care," she said.
The VBAC rate has dropped to 9.2 percent of births after a previous Caesarean in 2004, compared with 28.3 percent in 1996.
The rate of Caesareans among women who have not previously had one has shot up, climbing to 20.6 percent of such births in 2004, compared with 19.1 percent in 2003 and 14.6 in 1996.
Dr. Sarah Kilpatrick, head of a practice committee for the American College of Obstetricians and Gynecologists, said that 20 years ago, virtually no women asked for C-sections. But nowadays, she said, "the public gets the sense that it's like a zipper — they open you and then close you back up."
Some women believe they have a lower chance of becoming incontinent if they opt for a C-section, though the evidence to support that is not complete, Kilpatrick said.