A 29-year-old woman, gravida 1 para 0, at 26 weeks gestation comes to the office for a routine prenatal visit. She reports no contractions, vaginal bleeding, or leakage of fluid. There is good fetal movement. The patient has a history of polycystic ovarian syndrome. This pregnancy was conceived through ovulation induction but has otherwise been uncomplicated. She has no other chronic medical conditions or previous surgeries. The patient walks for 30-45 minutes 5 days a week. She takes prenatal vitamins and folate supplementation daily. She does not use tobacco, alcohol, or illicit drugs. Blood pressure is 130/80 mm Hg and pulse is 89/min. BMI is 27 kg/m². Fetal heart tones are 150/min. Fundal height is 28 cm. Third-trimester laboratory results are as follows: Testing of which of the following is the best next step in management of this patient?

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Explanation: 11ec2b69_bebb_77e3_8f63_377b9a187a67_MD0005_00 During the second and third trimesters, the placenta secretes increasing amounts of hormones (eg, human placental lactogen) that induce maternal insulin resistance. This insulin resistance ensures that there is a sufficient supply of glucose for fetal development. However, patients with inadequate pancreatic function are at risk for developing gestational diabetes mellitus (GDM). GDM is associated with obstetric (eg, preeclampsia) and neonatal (eg, hypoglycemia, polycythemia) complications. Patients with risk factors for undiagnosed pregestational type 2 DM (eg, obesity, prior macrosomic infant) are screened as early as the initial prenatal visit. Patients without risk factors are screened for GDM at 24-28 weeks gestation. A 2-step approach is involved in screening for GDM. The first step is a glucose challenge test (GCT), a screening test that consists of a blood glucose level measured an hour after administration of a 50-g glucose load. A blood glucose level >140 mg/dL is an indication for the second step, a 3-hour glucose tolerance test (GTT). The GTT is a diagnostic test that consists of a fasting blood glucose and blood glucose levels measured 1, 2, and 3 hours after a 100-g glucose load. GDM is diagnosed when >2 of the GTT values are elevated. This patient has an elevated GCT and requires a 3-hour GTT (Choice D). (Choice A) A fasting blood glucose level is not an effective diagnostic test for GDM. Fasting glucose levels are reserved as a second-line test for patients who cannot tolerate the GTT (eg, history of bariatric surgery). (Choice C) Hemoglobin A1c levels are lower in pregnant women due to physiologic increases in red blood cell mass and cell turnover. Therefore, a hemoglobin A1c is a less sensitive screening test for DM during pregnancy than a GCT. (Choice E) Monitoring of fasting and postprandial glucose levels is part of managing GDM and would be indicated if the GTT results were abnormal. Educational objective: Screening for gestational diabetes mellitus is performed at 24-28 weeks gestation with the 1-hour 50-g glucose challenge test. If the glucose challenge test result is elevated, the diagnosis of gestational diabetes mellitus is confirmed if a 3-hour 100-g glucose tolerance test is also abnormal. References: NIH consensus development conference: diagnosing gestational diabetes mellitus. (http://www.ncbi.nlm.nih.gov/pubmed/23748438) Practice bulletin no. 137: gestational diabetes mellitus. (http://www.ncbi.nlm.nih.gov/pubmed/23969827)

A 29-Year-Old Woman, Gravida 1 Para 0, at 26 Weeks