Despite widespread belief among both doctors and lay people that cerebral palsy results from lack of oxygen to the baby's brain during labor and delivery, a new report says that birth asphyxia alone accounts for 10 percent of cases at most.

The study found that the vast majority of children who develop cerebral palsy experience prenatal problems, including maternal infections, clotting disorders and strokes, that damage the developing brain long before labor begins.

The findings were described yesterday at a news conference in Albany held by the New York division of the American College of Obstetricians and Gynecologists, which has been concerned about the growing unwillingness of doctors to practice obstetrics because of litigation risks, skyrocketing jury awards and soaring rates of malpractice insurance.

The findings, based on hundreds of scientific studies, were compiled by an expert panel convened by the American College of Obstetricians and Gynecologists and the American Academy of Pediatrics. The report represents the first time in this country that all the variables and studies were analyzed in one place, and it ''clearly shows that there isn't one cause of cerebral palsy,'' said Dr. David Clark, a neonatologist at Albany Medical College.

The report, reviewed by 100 independent experts, was endorsed by a wide range of organizations, including the March of Dimes Birth Defects Foundation, the National Institute of Child Health and Human Development and the Centers for Disease Control and Prevention.

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Cerebral palsy is a relatively rare movement disorder that typically becomes apparent by the child's second or third year and affects about half a million Americans. There are several different forms of cerebral palsy, all of which involve uncontrollable movements and posture. Only one form, spasticity involving all four limbs, is related to lack of oxygen to the brain during birth.

Babies who develop cerebral palsy typically have symptoms at birth of neonatal encephalopathy, characterized by poor muscle tone and reflexes, difficulty waking up, breathing problems or seizures. Neonatal encephalopathy may or may not result in permanent brain damage.

Data summarized in the report were developed since the 1980's and are well known to many experts in maternal and fetal medicine, perinatology and pediatric neurology. But, the report's authors said yesterday, the true causes of cerebral palsy have yet to be recognized by most doctors, parents and lawyers.

Lawsuits with medical liability awards averaging $6 million and individual awards as high as $80 million for a birth with a poor outcome are prompting obstetrician-gynecologists in several states to leave obstetrics or to refuse to care for high-risk pregnancies.

In New York State, there are no doctors practicing obstetrics in 7 of the 62 counties, and nearly half those who completed obstetrical training in New York last year have left the state. Typically, 43 percent of a New York obstetrician's fee for delivering a baby goes toward malpractice insurance -- an average liability premium of $1,429 per delivery.

In an interview, Dr. Gary D. V. Hankins, an obstetrician-gynecologist at the University of Texas Medical Branch in Galveston who was chairman of the study group, said that when birth asphyxia occurred, organs other than the brain were also damaged, since the body preferentially shunted blood to the brain when oxygen was in short supply.

Possible causes of asphyxia in the birth process, he said, include premature separation of the placenta, strangulation by the umbilical cord, prolonged slowed fetal heart rate and inability of the baby's shoulders to pass through the birth canal. When such difficulties occur, he said, the baby must be delivered in 10 minutes or less to avert brain damage.

''Maybe half the cases can be prevented,'' he said. ''We can't prevent them all.'' When signs of fetal difficulties are detected at the onset of labor, Dr. Hankins offers several options, including a Caesarean delivery, which the overwhelming majority of patients accept. But, he said, ''I have to do 500 Caesareans to prevent one case of cerebral palsy.''

The belief that birth asphyxia is the cause of cerebral palsy dates to the 1860's when an English surgeon, William Little, first described a condition of stiff, spastic muscles in young children, many of whom were born after premature or complicated deliveries. Dr. Little suggested that their condition resulted from a lack of oxygen at birth.

This notion stuck despite Sigmund Freud's disclaimer in 1897 that ''difficult birth, in certain cases, is merely a symptom of deeper effects that influence the development of the fetus.'' Freud, who observed that affected children often had other problems, like mental retardation, visual disorders and seizures, believed the disorder had roots during the brain's development in the womb.

Dr. Frank Miller, a professor of obstetrics and gynecology at the University of Kentucky in Lexington, who appointed the study group, said, ''Birth asphyxia was one of those myths we all thought was true -- it was what most obstetricians and pediatricians were taught in the past.'' The new report states, ''Historically, the incorrect assumption that virtually all cases of neonatal encephalopathy resulted from intrapartum asphyxia impeded the search for other causes, especially causes arising before the onset of labor.''

Nearly a century later, scientists analyzed an extraordinary collection of data from more than 35,000 births that occurred from 1959 through 1966. Findings published in a pediatric journal in the 1980's from this government-sponsored Collaborative Perinatal Project revealed that only a fraction of cases of cerebral palsy -- probably less than 10 percent -- could be traced to an oxygen shortage at birth and that no cause was apparent in the majority of cases. The findings were not well publicized at the time.

In the decades since, new techniques, including sonograms, CT scans, M.R.I.'s and fetal monitoring, have revealed a host of other explanations for brain-injured babies, mainly damage that occurs during the pregnancy, long before labor begins. One of the most common, according to a report in 2000 by Dr. Yvonne W. Wu, a pediatric neurologist at the University of California in San Francisco, is chorioamnionitis, a maternal infection of the chorion and amniotic fluid that elicits an inflammatory response by the fetus. The resulting substances, called cytokines, are toxic to cells in the fetal brain that control motor fibers in the legs, Dr. Wu said in an interview.

Full-term infants exposed to this infection face a fivefold increased risk for cerebral palsy, she said.

Another common cause of cerebral palsy is premature birth, which may actually result from an intrauterine problem, like infection. Other causative factors include intrauterine growth retardation, coagulation disorders that cause clots (prenatal strokes) or bleeding in the fetal brain, metabolic disorders, chromosomal abnormalities, cerebral malformations, among other prenatal conditions. In some cases, the pre-existing condition compromises the baby's ability to withstand the stresses of labor and delivery, further compounding the brain injury.

''We're not saying that there are no valid cases for litigation,'' said Dr. Mary E. D'Alton, chairwoman of obstetrics and gynecology at Columbia-Presbyterian Medical Center in New York. ''It's just that the day of delivery is but one day in a 280-day gestation period, during which lots of complications can occur that damage the fetal brain.''

The new report lists four essential criteria, all of which must be met, to attribute a case of cerebral palsy to birth asphyxia, plus five other criteria indicating an asphyxia injury. The report concludes that neonatal encephalopathy resulting from asphyxia in labor and delivery occurs about 1.6 times in 10,000 births.

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