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Mon 12 Nov 2007 04:21 PM

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Getting to grips with gestational diabetes

Dealing with gestational diabetes, a glucose intolerance diagnosed during pregnancy, requires a careful balancing act.

Gestational diabetes is glucose intolerance diagnosed while a woman is pregnant, usually late in the second trimester or in the third. The disease, like other forms of diabetes, affects how the body handles sugar, and the result in this case is that too much sugar remains in the bloodstream. Gestational diabetes raises the risk of complications during delivery.

In normal digestion, the sugar molecule glucose-an important source of energy-is absorbed into cells with the help of insulin, produced by the pancreas gland. During pregnancy, the placenta secretes a hormone called human placental lactogen to protect the foetus and make sure it receives enough energy even if the mother fails to.

Gestational diabetes raises the risk of complications during delivery.

The hormones make it harder for the mother's cells to absorb glucose because they raise her resistance to insulin. Thus, too much sugar may stay in her blood. Her insulin resistance may increase during pregnancy as the placenta grows and produces more of the offending hormones.

Rhonda Bentley-Lewis, MD, an endocrinologist at Harvard Medical School and Brigham and Women's Hospital, says that about 4% of pregnant women are diagnosed with gestational diabetes. Its prevalence can range from 1 to 14%, depending on risk factors.

Women at risk include those who are over 25, overweight before pregnancy, have first-degree relatives with type II diabetes (the most common form, in which either the body does not produce enough insulin or the cells ignore the insulin), and who have had gestational diabetes during past pregnancies.

Most pregnant women in the US are tested for gestational diabetes as a regular part of their prenatal care.

Simple test for diagnosis

A woman with gestational diabetes will likely not exhibit symptoms, though she may show signs of polyuria (urinating too much liquid) or polyphagia (excessive hunger or eating) if she has type II diabetes that has gone undiagnosed. Diagnosis of gestational diabetes usually happens between weeks 24 to 28 of gestation, though Bentley-Lewis says there's a movement towards screening for it during the first trimester for women in high-risk groups.

Women start by taking one of two tests, called the one-hour glucose challenge. They drink a 50-gram glucose beverage, such as a carbonated soda or a syrupy solution. An hour later, their blood is drawn to measure blood-sugar levels. A glucose level around 130 to 140 milligrams per deciliter (mg/dL) is considered normal, says Bentley-Lewis, though different clinics' cut-offs may vary. Patients do not fast before this test.

A blood-sugar level higher than 140 mg/dL means they should do a second test, the 100-gram glucose challenge. To prepare for this test, a woman must fast for eight to 10 hours overnight, after which her blood is drawn for a glucose test. She then drinks a 100-gram glucose beverage, and doctors draw blood to test sugar levels three more times, at one, two, and three hours later. The blood-sugar threshold values doctors look for at each step are as follows:

• 95 mg/dL after fasting
• 180 mg/dL after one hour
• 155 mg/dL after two hours
• 140 mg/dL after three hours

If a woman's blood sugar hits two or more of these levels, she is diagnosed with gestational diabetes. These levels are based on criteria established in a 1982 study by doctors Carpenter and Coustan. Some clinics rely on diagnostic criteria from the National Diabetes Data Group, which has higher thresholds for normal and abnormal results.

Difficult balance for treatment

"The first line of defence is always diet and physical activity," says Bentley-Lewis, even for pregnant women found to have type II diabetes during testing. However, she cautions, "These are pregnant women, so we need to balance the goals of adequate nutrition for the foetus with restricted carbohydrates for the mother."

This can be a difficult balance. And Bentley-Lewis says that lifestyle changes-be it fewer calories, more fruit and vegetables, longer walks, etc-are best determined on an individual basis in conversations between the patient, her doctor, and a counsellor on nutrition, such as a registered dietician.

During the remainder of the pregnancy, women and their physicians continue to monitor glucose levels, which should be around 100 mg/dL pre-meal and 100-129 mg/dL after eating. For between 30 and 50% of women, diet and exercise simply don't do the job, and these women will require medical therapy to control their sugar levels.

Some doctors prescribe oral medication such as glyburide, which lowers blood sugar by stimulating the pancreas to secrete insulin. One study has found it to be at least as effective as insulin.

But Bentley-Lewis says this drug is used only occasionally and with caution, with most physicians preferring to prescribe insulin. Though doctors now use synthetically made human insulin as opposed to pork or beef insulin, it is still prepared with additives that in rare cases can cause an allergic reaction.

What are the complications of gestational diabetes?

There can be delivery complications for women with gestational diabetes. Babies who receive excess glucose may be larger than normal, and their shoulders could get lodged or pinned during a vaginal birth. This could make delivery unsafe for both the mother and baby. A large baby puts a mother at risk for post-partum haemorrhaging because of the increased size of her uterus.

Babies are at risk for low blood sugar (hypoglycemia) soon after they're born because they make more insulin than normal and are no longer exposed to the increased amount of glucose from their mothers. This puts them at risk for developing obesity and type II diabetes when they grow older. An excess of glucose in the womb could also cause a delay of lung growth and maturity, which could lead to breathing problems, says Bentley-Lewis.

After delivery, women should continue to check in with their obstetrician or endocrinologist every few weeks, and they should be screened for diabetes annually. As during pregnancy, there's no particular regimen a woman should follow to remain healthy; this depends on the mother's overall health and her doctor's recommendations. The diabetes usually goes away after pregnancy, but women are at risk for developing it during their next pregnancy and also for developing type II diabetes. And if a woman has diabetes, says Bentley-Lewis, this increases her risk of cardiovascular disease.

This article is provided courtesy of Harvard Medical International. © 2007 President and Fellows of Harvard College.

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