Gestational Diabetes

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Gestational diabetes is diabetes that develops during pregnancy in someone who did not have diabetes prior to becoming pregnant. This can happen because the hormonal changes during pregnancy cause pregnant women to become more resistant to insulin, the hormone that keeps blood sugar levels under control. This insulin resistance results in the need for the pancreas to make more insulin, and some women cannot make enough insulin to meet that need. The prevalence of gestational diabetes in the U.S. has been estimated to be between 5.6% to 9.2% from 2007 to 2016, but may be up to three times higher, depending on the diagnostic criteria used. Gestational diabetes typically develops in the second or third trimester. Women who have a new diagnosis of gestational diabetes in the first trimester most likely had pre-existing, undiagnosed, type II diabetes. Gestational diabetes increases the risk of preeclampsia, infants that are larger than average size (fetal macrosomia), birth injury or shoulder dystocia (a complicated type of delivery), and caesarean delivery.

Screening for diabetes, especially type II, used to rely of glucose tolerance tests but now uses Hemoglobin A1c levels to diagnose diabetes. Oddly enough, this does not work for screening for gestational diabetes as A1c levels have been found to have both low specificity and sensitivity to diagnose gestational diabetes. Therefore, screening for gestational diabetes relies on the old-fashioned oral glucose challenge or tolerance tests. This involves having the patient drink a specific amount of glucose (usually 50 g or 75 g) and then measure glucose levels at set intervals. This screening is usually performed in the second trimester between 24 and 28 weeks of gestation. The U.S. Preventive Services Task Force (USPSTF) recently published their recommendation that asymptomatic pregnant women should be screened for gestational diabetes at or after 24 weeks of gestation. They also concluded that available evidence was insufficient to recommend screening before 24 weeks. This recommendation applies to women who were not previously diagnosed with type I or II diabetes.

The goal of screening is to identify and treat gestational diabetes earlier rather than later thereby lessening the risk of adverse maternal or fetal outcomes. The harms of screening are few but can include psychological stress as well as increased medical monitoring and interventions (especially during labor, delivery, and the immediate post-partum period) that come with having a diagnosis of gestational diabetes. There is also a potential risk of low blood sugar in both the mother and infant as a result of treatment, but this is uncommon. As for treatment of gestational diabetes, it includes lifestyles modifications (diet and exercise) and, in some cases, the use of insulin injections.

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 By Peter Galvin, MD

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