With the increased use of ultrasound as a diagnostic tool, especially in obstetrics, comes an increasing danger for physicians -- lawsuits stemming from misreading the sonogram or failure to use ultrasound when there were indications that it should have been used.

"Nearly every obstetrician is buying ultrasound equipment for the office," says Dr. Roger C. Sanders, associate professor of radiology and obstetrics at Johns Hopkins University who has tracked all legal cases involving ultrasound in the United States -- a total of 135, most of which involved obstetrical issues.

"Many women are now insisting on it being done. And a large number of studies are being performed by people who are relatively untrained in the field. It's not easy (to read a sonogram)."

Sanders and six other ultrasound experts spoke at a recent conference on "Diagnostic Ultrasound in Obstetrics and Gynecology" sponsored by Johns Hopkins in Baltimore. About 150 doctors, nurses and technicians attended the two-day conference, which examined clinical problems in the field of ultrasound, including diagnosis of hydrocephalus, use in the first trimester, breast ultrasound to detect tumors, measurement of fetal growth, and legal and ethical questions.

Diagnostic ultrasound (also called sonography) involves taking pictures of internal body structures using sound waves. The reflection of sound energy off water and tissues is translated into a photographic image. The technique is widely used to look at fetuses.

Sanders said in an interview after the conference that the most frequent source of legal problems involves a missed ultrasonic diagnosis. Missing a case of ectopic pregnancy, in which a fertilized egg implants itself in a fallopian tube instead of in the uterus, endangering the woman's health, is the most frequent problem. Ectopic pregnancies are hard to see, Sanders said, because the lining of the uterus can look just like it does early in a normal pregnancy.

The next most common problems are failure to diagnose the presence of twins and failure to spot deformed fetuses. "The mother has a baby that is malformed and looks for someone to blame." Sanders said.

Another danger area is failure to diagnose placenta previa, in which the placenta is situated over the cervix, blocking the baby's exit.

The most rapidly growing source of problems, Sanders said, stems from failure to perform ultrasound when it was clinically indicated, where there was high risk for fetal growth retardation or multiple pregnancy, or where there was unexplained vaginal bleeding or previous ectopic pregnancies, for example.

Of the 135 legal actions arising from ultrasound that Sanders has studied, only one has made it to trial. That one involved a diagnosis of placenta previa in a Miami area woman. The records were sent to the wrong clinic, the mother suffered severe bleeding, Sanders said, and the award was over $1 million.

Most of the cases so far have been settled out of court.

Sanders said suits involving fetuses or infants can be particularly expensive for physicians, with damages often running into the millions of dollars because the awards are based on estimated medical expenses until the child is 18.

There is currently no certification process for medical practitioners who use ultrasound, Sanders said. "I'm anxious to get one instituted."

A conference committee from the American College of Obstetricians and Gynecologists, the American College of Radiology and the American Institute of Ultrasound in Medicine has drawn up recommendations for a minimum level of ultrasound training. Sanders said the committee recommended one month of formal training and two months of performing ultrasound examinations, at least 200, consulting regularly with more experienced doctors and not charging a fee.

But many of those who use ultrasound equipment do not have that minimum level of training, Sanders said. And for the health care consumer, there is no easy way to find out whether an obstetrician has been sufficiently trained in taking and reading sonograms.

"Ask around is the best advice I can give," he said, "and see how professional is the way in which the films are taken. If you've had ultrasound before, you should have some basis for comparison."

Routine use of ultrasound in pregnancy is a matter of debate among obstetricians. Recently, the National Institutes of Health recommended that it be used only when there is a specific medical reason and issued a list of 28 situations in which it could be justified.

One relatively new area for the use of ultrasound is in treatment of infertility by determining the best time to administer egg-producing hormones and in the timing of conception. "You can see whether there is an egg at all," Sanders said. And the egg can be measured. "When it gets to a certain size, you can say that's the time to have intercourse."

Ultrasound is also being used with in vitro, or test tube, fertilization to help remove the eggs.