The chances a woman will give birth through Caesarean section appears to depend much more on who her doctor is than other criteria, a new study concluded Wednesday.

Dr. Gregory Goyert and his colleagues at the Sinai Hospital of Detroit studied 1,533 women who had babies at a community hospital in an affluent Detroit suburb in 1986 and 1987.The researchers reported in The New England Journal of Medicine that the 11 doctors who performed the deliveries varied widely in how likely they were to use Caesarean sections even though their patients did not vary significantly.

The chances a woman in the study would have a Caesarean varied from one in three to one in 10, depending on who her doctor was, the researchers said.

"We conclude that individual practice style may be an important determinant of the wide variations in the rates of Caesarean delivery among obstetricians," the researchers wrote.

"We believe that the effect of this `physician factor' in determining the method of delivery has previously been either underappreciated or underreported," they said.

The identity of the physician was second only to whether the woman was having her first baby in being the most important factor determining whether she had a Caesarean, the researchers said. The doctor's identity was an even more likely factor than the baby's weight, which is usually an important factor in deciding whether to perform a Caesarean, the researchers said.

The difference among the doctors could not be explained by the types of patients they were seeing or any other major factors, the researchers said.

The study also found the babies delivered through Caesarean did not do significantly better than those who were not, suggesting that many of the procedures were unnecessary.

"We were unable to demonstrate objective evidence that higher Caesarean-section rates reduce neonatal morbidity, which was rare in this low-risk population," the researchers wrote.

Caesarean sections involve surgically removing the baby from the womb through an incision in the abdomen instead of delivering the child through the natural birth canal.