Experts divided on early, universal screening for GD
No such thing as a no-risk woman’
(Diabetes Management continues to feature the effects of the disease from the perspectives of different types of patients. This month, the newsletter looks at the special concerns for female patients.)
Experts know to keep an eye out for gestational diabetes (GD) during a patient’s pregnancy. And just about every pregnant woman is at risk of developing it, says endocrinologist Lois Jovanovic, MD, director and chief scientific officer at Samsun Medical Research Institute in Santa Barbara, CA.
"Unless she’s very young, very thin, doesn’t display any signs of impaired glucose tolerance, doesn’t belong to any minority group, and doesn’t have any relatives with diabetes, she’s at risk," says Jovanovic. "Even those considered at the lowest possible risk still have a 2% risk of developing GD. There’s no such thing as a no-risk woman."
That’s why Jovanovic says she is a strong proponent of universal and early screening. "It’s no big deal to do a blood test. It costs about $7, and that’s not much to avoid the risk of complications that are rampant in undiagnosed GD."
She points out that California still mandates a rubella screening for each pregnant woman, at a cost of $43, even though there have been no cases of rubella in the state in the past 10 years. Therefore, she says, a $7 test that could prevent future grief for both mother and child is "a wise investment."
While the American Diabetes Association (ADA) recommends GD screening for at-risk women between the 24th and 28th weeks of pregnancy, Jovanovic says that may be too late. "If they even smell or look like they have diabetes, screen them the first time you meet them."
Samsun is proud of its eight-year record without fetal loss due to GD. "You’ll never see a sugar-related birth problem if you take care and don’t miss anybody," says Jovanovic.
GD is most likely caused by increasing insulin demands of the fetus on the placental hormones as the fetus grows. In women with impaired glucose tolerance, the rapidly increasing insulin demand cannot be met, swinging them and their babies into hyperglycemia.
Because of its cumulative effect, early screening for GD is "totally worthless," counters E. Albert Reece, MD, Abraham Roth professor and chairman of the department of obstetrics, gynecology and reproductive sciences at Temple University in Philadelphia. He notes studies which show that by the middle of the third trimester, 85% of cases of GD will present themselves and nearly 100% will be apparent by the 34th week.
Some obstetricians will choose to deliver a viable baby as early as possible by cesarean if there are indications of macrosomia.
Screening based on risk factors is not particularly effective, agrees Marshall W. Carpenter, MD, assistant professor of obstetrics and gynecology at Brown University in Providence, RI. Carpenter sat on the ADA consensus committee that helped draw up the clinical guidelines for GD. Before the 24th week, he says, tests may not be conclusive.
"The delay was based on the observation that many people have a normal screening test value if it is done early," says Carpenter. "And we don’t know if early identification would improve our chances of moderating the effects of GD."
At the heart of the debate is the fine line between Type 2 diabetes and gestational diabetes. While women who have diabetes should undergo rigorous preconception counseling (see p. 17), undiagnosed women or women with diagnosed impaired glucose tolerance could move into full-blown diabetes at any time, says Reece. They are particularly vulnerable at times of hormonal turmoil, like in pregnancy, and may not know they are diabetic until it is too late to stop birth defects that most often occur in the first eight weeks of pregnancy — a time when they may not even know they are pregnant. (See article on birth defects, at right.)
Approximately 5% of all pregnant women develop GD. Undiagnosed and/or untreated gestational diabetes can lead to macrosomia or large birth weight babies who are at high risk for obesity later in life and have a high potential for developing diabetes themselves.
"With poorly controlled GD, there is a chance of fetal obesity caused by a high level of blood insulin," says Carpenter.
So, as in all types of diabetes, tight control is the answer. Diet, exercise and, ultimately, insulin are the approved means of controlling blood sugars in patients with GD.
It takes a team to give the right care
Jovanovic says a diabetes team is essential to a successful conclusion to any pregnancy where gestational diabetes is involved. "An OB/GYN has very little time or information about diet and the best type of control to ensure a safe delivery and continued health for the mother," says Jovanovic. "That’s where the diabetes team comes into play with all the health care professionals she needs to help her deliver a normal-weight, healthy baby and to avoid a later onset of Type 2 diabetes."
Unpublished data from Brown University in Providence, RI, indicate an estimated 2% to 2.9% of women with GD generally return to normoglycemia after their pregnancies. However, their risk of developing Type 2 diabetes later in life is dramatically increased. Risk assessment data for the development of Type 2 varies from study to study, but it ranges from 17% to 63% within five to 16 years after pregnancy.
As with all types of diabetes, weight control will go a long way toward preventing the onset of Type 2 disease, says Carpenter. "But frequent postpartum monitoring will also let us know if there is a problem developing."
ADA guidelines recommend a fasting blood glucose test six weeks postpartum for all women with GD and then monitoring at least every three years afterward. More frequent monitoring and early intervention are recommended for women who have impaired fasting glucose.
[Contact Lois Jovanovic at (805) 682-7838, Marshall Carpenter at (401) 863-1000, and E. Albert Reece at (215) 707-3002.] n