TORONTO - Many women as they head into their final weeks of pregnancy wonder whether their own obstetrician will deliver the baby or whether the doctor will be someone else on call at the time.

A study of deliveries at a Montreal hospital attempted to answer the question, and also looked at how outcomes might vary. Almost 77 per cent of deliveries were by the patient's own obstetrician, and 23 per cent by the on-call obstetrician, according to the findings, published in the latest edition of the Canadian Medical Association Journal.

The researchers looked at all live single-term births between 1991 and 2001 at Royal Victoria Hospital in Montreal - a total of more than 28,000 eligible deliveries attended by 26 obstetricians.

"What we wanted to do was address the question of whether or not it made a difference to the patient and the obstetrical care in general, whether or not patients were delivered by their own doctor or by an obstetrician taking part in a call group," one of the study's authors, Dr. Haim Abenhaim, said from Montreal, where he's an obstetrician at Sainte-Justine Hospital.

He noted that there's an evolution in Canada toward obstetricians taking part in call groups to provide obstetrical care.

"They take turns in spending the night either in the case room or responsible for the care of obstetrical patients for a given time period. And they rotate that kind of care."

The researchers found that the women attended by an on-call obstetrician had a higher rate of caesarean delivery - 11.9 per cent versus 11.4 per cent.

"The difference was really marginal. It was a very small difference in risk," said Abenhaim.

They also found that the women attended by on-call obstetricians had higher rates of third-or fourth-degree tears (7.9 per cent versus 6.4 per cent) and lower rates of episiotomy, a surgical cut made at the opening of the vagina to aid delivery (38 per cent versus 43 per cent).

"When we look at the absolute numbers, they weren't enormous enough for us to feel that they actually make an important enough difference to change the way that we provide obstetrical care," Abenhaim said.

"We think that overall, patients shouldn't be deciding on who they should go (to) for their obstetrical care based on the fact that they'll be attending their delivery, but rather they should be looking to see an obstetrician that will be more likely to have a good rapport with them."

It was found that the higher overall rate of C-section delivery by on-call obstetricians was due mainly to nonreassuring fetal heart tracing during the first stage of labour.

Dr. Chaim Bell, who wrote a commentary for the journal, said it could be because the on-call obstetricians are around the machines more and might rely on them more. And, he said, it raises questions about how good fetal heart rate tracing is in identifying babies in distress.

"We think that it identifies babies that are going to do badly," said Bell, who works as a general internist at St. Michael's Hospital in Toronto, and does research on continuity of care.

"But in fact it has a very high false positive rate, meaning that when you think it's positive, when you think there's an abnormality there, for the most part nothing really happens."

The researchers and Bell both hypothesized that concern over medical malpractice might cause on-call obstetricians to manage delivery differently for women who aren't under their regular care.

But overall, Bell said the differences highlighted in the study are small and "not a cause for worry."

However, because the delivering doctor may not be the one a woman has seen throughout her pregnancy, Bell urged women to ensure that relevant health records are transferred to the delivery area of the hospital where the birth is to take place.

In Ontario, he said, this normally takes place around the 28th to 30th week of pregnancy.

"Make sure that you have knowledge of your history, the medical history and that you can provide that and all the salient features to the obstetrician," he urged.

Abenhaim said the study did not look at deliveries by family doctors. Another study, coming out in October, will look at outcomes of vaginal deliveries among obstetricians and family doctors, he said.