Causes of Gestational Diabetes

Like the other types of diabetes, the exact cause of gestational diabetes is unknown. However, experts do have some clues.

During pregnancy, the placenta, which is the organ that nourishes the growing baby,  produces large amounts of various hormones.  Hormones are important for the baby’s growth.

However, these hormones may also block insulin’s action in the mother’s body, causing insulin resistance. All pregnant women have some degree of insulin resistance.

Gestational diabetes usually appears around the 24th week of pregnancy. This is when the placenta begins producing large quantities of the hormones that cause insulin resistance. The period between the 24th and 28th weeks of pregnancy is the usual time to screen for gestational diabetes.

Because insulin resistance seems to cause gestational diabetes, it is more like type 2 diabetes than type 1 diabetes. And having gestational diabetes increases your chances of someday developing type 2 diabetes (but not of developing type 1 diabetes).

Historical Perspective
For thousands of years, doctors have recognized diabetes as a disease, but did not understand its cause. An early Egyptian medical text written around 1550 B.C., called the Ebers Papyrus, describes a condition of “passing too much urine.” The Greek physician Aretaeus, who lived in the second century A.D., gave diabetes its name, from a Greek word meaning “siphon” or “pass through.” Aretaeus observed that his patients’ bodies appeared to “melt down” into urine.

People observed early on that the urine from people with diabetes was very sweet. In fact, one way to diagnose diabetes was to pour urine near an anthill. If the ants were attracted to the urine, it meant that the urine contained sugar. By the 18th century, physicians added the Latin term mellitus to diabetes, which describes its sugary taste.

In 1776, scientists discovered that the glucose was in the blood of both people with diabetes and people without diabetes. That led them to suspect that people with diabetes pass glucose from the blood to the urine. But they didn’t know how.

Then in 1889-more than 100 years after glucose was found in blood-two German physiologists, Oskar Minkowski and Joseph von Mering, found quite by accident that the pancreas was involved in diabetes. While studying how fat is metabolized in the body, they decided to remove the pancreas from a laboratory dog.

Much to their astonishment, the dog urinated again and again.

Proving that science rewards a prepared mind, the scientists had the foresight to test the dog’s urine for glucose. Sure enough, the dog had developed diabetes when its pancreas was removed.

This led the scientists to suspect that some substance in the pancreas somehow prevented diabetes. As scientists embarked on a 30-year quest to find that magic substance, people with diabetes were subjected to a host of so-called cures, including bloodletting, opium, and special diets. Unfortunately, none of these measures helped the disease. Although some diets did seem to help some older people with diabetes, they did nothing for severely affected young patients. These patients typically died within several years of developing the disease.

In 1921, Dr. Frederick Banting, a young surgeon just out of medical school, had a breakthrough. He had the idea to isolate the groups of cells called the islets of Langerhans in the pancreas. Banting began his experiments working in the laboratory of a senior faculty member at the University of Toronto, Professor J. J. R. Macleod, an authority on carbohydrate metabolism. Macleod teamed Banting with a young medical student named Charles Best.

Using experimental dogs, Banting’s approach was to tie off the pancreatic duct-which connects the pancreas to the intestine.

This would destroy most of the tissue of the pancreas, which would no longer be able to secrete its digestive enzymes into the intestine. Banting guessed that the islets of Langerhans secrete something directly into the blood and that these cells would survive. At long last, Banting and Best succeeded in treating a dog with diabetes using extract from the islet cells.

Within 6 months after their success with the diabetic dog, the two scientists injected their extract into Leonard Thompson, a 14-year-old boy who was dying from diabetes, but the boy remained ill. A biochemist working in Macleod’s laboratory, J. B. Collip, purified the extract, and the experiment was repeated 12 days later. This time the scientists succeeded, and Thompson, emaciated from diabetes, began to gain weight and lived for 15 years with regular insulin injections, until he died from pneumonia. In 1923, Banting and Macleod were awarded the Nobel Prize in Medicine for their discovery. Feeling that their collaborators had been slighted, Banting shared his prize money with Best, and Macleod shared with Collip. The team had made an important discovery leading to a diabetes treatment that is still in use today.

Researchers suspect that the genes responsible for type 2 diabetes and for gestational diabetes may be similar.

Gestational diabetes is more common in groups that have more obesity. Obesity can trigger gestational diabetes as well as type 2 diabetes.

Some women show signs of high blood glucose even before the 28th week of pregnancy. It is likely that these women had diabetes that was not recognized before pregnancy. The weight gain and hormonal changes of pregnancy stressed the body and revealed the diabetes. After the pregnancy, these women need to be tested for diabetes, and either type 1 or type 2 diabetes may be diagnosed.

Martha M. Funnell, MS, RN, CDE
Michigan Diabetes Research and Training Center
University of Michigan Medical School
Ann Arbor, Michigan

Robert M. Anderson, EdD
Michigan Diabetes Research and Training Center
University of Michigan Medical School
Ann Arbor, Michigan

Shereen Arent, JD
National Director of Legal Advocacy
American Diabetes Association

American Diabetes Association Complete Guide to Diabetes

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