Get experienced help for unexpected shoulder dystocia. (Without Macrosomia).

CANCUN, MEXICO -- Macrosomia is not the only route to shoulder dystocia.

"The problem with shoulder dystocia is that not all cases involve babies who are more than 4,500 g or even more than 4,000 g," Dr. John T. Queenan said at a conference on obstetrics, gynecology perinatal medicine, neonatology and the law.

'About 40%-50% of shoulder dystocia cases involve babies without macrosomia"--a mother with an abnormally shaped pelvis, for example--which means that "no matter what an obstetrician does, there occasionally will be infants born with shoulder dystocia," he noted.

It's these unanticipated cases of shoulder dystocia that can cause real trouble. "V/hen a fetus is more than 4,500 g you can make plans, but with smaller babies you won't know until it occurs. It's virtually impossible to screen for all shoulder dystocia," said Dr. Queenan, professor of ob.gyn. at Georgetown University, Washington.

The upshot is that shoulder dystocia is bound to appear unexpectedly and when it does it's a "true medical emergency" that requires an obstetrician to get all the help available, he said.

"Once shoulder dystocia occurs, the physician ...