Getting women into medical care when they are only a few months pregnant is a top priority of public health officials, because simple interventions often save the lives of both mother and child.

Early treatment for H.I.V., syphilis and high blood pressure, as well as vaccines like tetanus and vitamins like folic acid, can make enormous differences in whether mother and baby survive the birth.

But poorly educated women often think it is not worth the trouble to visit a clinic before they are in labor. Many believe that consulting traditional healers is just as worthwhile.

Now a group of Canadian doctors is pioneering what appears to be a very effective way to entice rural African mothers to visit clinics long before their due dates. They offered ultrasounds advertised on local radio with the words: “You will be able to see your baby.”

The medical charity Bridge to Health Medical and Dental tested the concept in the highlands of southwest Uganda in 2014. Their study, published by PLOS One this year, found that when doctors set up temporary clinics in rural villages, six times as many pregnant women visited when free ultrasounds were advertised, compared with the turnout in villages where the ultrasounds were not offered or were advertised only by word of mouth.

Women who previously had seen only traditional healers were nine times more likely to show up if the ultrasounds were advertised.

“It’s magic to be able to see your unborn baby,” said Dr. Michael S. Silverman, an infectious disease specialist at Western University in London, Canada, and a study co-author.

The ultrasound scanners in the study cost $10,000 new or $2,500 refurbished, said Dr. William Cherniak, the executive director of Bridge to Health and another co-author. They are battery-powered, do 40 scans per charge, and can survive bouncing along rutted dirt roads.

The group hopes to test inexpensive new scanners that plug directly into smartphones; the technician can view the fetus on the phone and transmit the image to a radiologist anywhere in the world, Dr. Cherniak said.

The women in the study could see their fetuses only on monitors, but Bridge to Health has since added a printer so the women can take home pictures.

“We even diagnosed acute appendicitis in an older woman who came in even though she wasn’t pregnant,” Dr. Cherniak said. “These machines have lots of uses.”