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Am Fam Physician. 2009;80(2):185-186

See related editorial on page 132.

Case Study

A 29-year-old woman at 20 weeks' gestation visits your office for a routine prenatal examination. This is her second pregnancy, and she has gained 15 lb (6.8 kg). According to her medical record, the patient's prepregnancy body mass index (BMI) was 27 kg per m2. She mentions that her father was recently diagnosed with diabetes, and she asks whether she should be tested for diabetes.

Case Study Questions

  1. Based on the U.S. Preventive Services Task Force (USPSTF) recommendation on screening for gestational diabetes mellitus, what is the most appropriate approach to this patient?

    A. Screen for gestational diabetes at this visit with a one-hour oral glucose challenge test.

    B. Schedule a three-hour oral glucose tolerance test at her 24-week visit.

    C. Explain the risk factors for gestational diabetes, and discuss potential benefits and harms of screening.

    D. Do not screen for gestational diabetes because she did not have gestational diabetes with her first pregnancy or pregestational diabetes.

    E. Do not screen for gestational diabetes because a false-positive test could cause prolonged psychological harm.

  2. Which one of the following statements is the best assessment of the patient's risk of gestational diabetes?

    A. She is at increased risk if she is white.

    B. Her age puts her at lower risk of gestational diabetes.

    C. She is not at increased risk because she did not have gestational diabetes in her previous pregnancy.

    D. Her age and prepregnancy BMI increase her risk of gestational diabetes fivefold.

    E. Her prepregnancy BMI increases her risk of gestational diabetes.

  3. Which of the following approaches to gestational diabetes prevention is/are recommended for this patient?

    A. Encourage participation in physical activity.

    B. Counsel her on achieving appropriate weight gain based on her prepregnancy BMI.

    C. Prescribe an oral hypoglycemic agent.

    D. Recommend an appropriate diet to regulate her blood sugar.


1. The correct answer is C. The USPSTF found insufficient evidence to assess the balance of benefits and harms of screening pregnant women for gestational diabetes mellitus before or after 24 weeks' gestation. It is not known whether screening for gestational diabetes improves health outcomes for mothers or infants; therefore, physicians and patients should make decisions on a case-by-case basis. Although positive screening results are common, fewer than one in five women with an abnormal glucose challenge test will meet criteria for gestational diabetes with an oral glucose tolerance test.

Women with diabetes diagnosed before pregnancy (pregestational diabetes) are at increased risk of maternal and fetal complications; however, the degree to which pregnant women with gestational diabetes are at increased risk of complications is less certain. The evidence is poor to determine whether important health outcomes such as mortality, brachial plexus injury, clavicular fracture, or admission to the neonatal intensive care unit are reduced by screening for gestational diabetes after 24 weeks' gestation.

In the United States, the most common laboratory screening test for gestational diabetes is the 50-g one-hour glucose challenge test. Most screening occurs between 24 and 28 weeks' gestation. There is little evidence on the value of screening earlier in pregnancy. If the glucose challenge test result is abnormal, the patient should undergo a 100-g three-hour oral glucose tolerance test to confirm the diagnosis of gestational diabetes.

Available evidence suggests that potential psychological and physical harms of gestational diabetes screening, such as short-term anxiety, do not persist late into the third trimester.

2. The correct answer is E. Without a history of previous gestational diabetes or a family history of diabetes, a woman is considered to be at low risk of gestational diabetes if all of the following factors apply: white ethnic origin, BMI less than 25 kg per m2, and age younger than 25 years. This patient is at increased risk of gestational diabetes because of her family history of diabetes, her age, and her prepregnancy BMI. Women of certain ethnic groups (e.g., Hispanics, American Indians, Asians, blacks) are at increased risk of gestational diabetes. Although women at low risk are less likely to benefit from screening for gestational diabetes, the absolute difference in the prevalence of gestational diabetes between low-risk patients (1.4 to 2.8 percent) and high-risk patients (3.3 to 6.1 percent) is relatively small.

3. The correct answers are A and B. Nearly all pregnant women should be encouraged to participate in moderate physical activity and to achieve moderate weight gain based on their prepregnancy BMI. Healthy pregnancy weight gain for women at normal weight is 25 to 35 lb (11.3 to 15.8 kg). Women who are overweight or obese should gain less weight.

For a confirmed diagnosis of gestational diabetes, treatment options include dietary management, physical activity, oral hypoglycemic agents, insulin, and insulin analogues.

This series is coordinated by Joanna Drowos, DO, contributing editor.

A collection of Putting Prevention Into Practice published in AFP is available at

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