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Case Study: A 34-Year-Old Woman in Her Second Pregnancy at 24 Weeks Gestation
Steven G. Gabbe, MD
The findings of significant glycosuria should prompt the performance of a glucose determination before the patient leaves the clinic. The usual approach to screening would be a 50-g oral glucose load administered to the patient between 24 and 28 weeks gestation when the "diabetigenic stress" of pregnancy is present. A positive test is a venous plasma glucose value 1 hour later of > 140 mg/dl. This would lead to a 100-gm oral glucose tolerance test (OGTT) with the diagnosis of GDM made if two of the following values are met or exceeded: fasting, 95 mg/dl; 1-hour, 180 mg/dl; 2-hour, 155 mg/dl; and 3-hour, 140 mg/dl. These cutoff values are those proposed by Carpenter and Coustan and recommended most recently by the Fourth International Workshop-Conference on Gestational Diabetes Mellitus and the American Diabetes Association.
The patient's capillary glucose reading, performed in the clinic, was 193 mg/dl. She was instructed to return the next morning for a fasting venous plasma glucose, which was 143 mg/dl. Given this finding, the diagnosis of GDM was established. While it is likely that the patient had diabetes before pregnancy, given the significant elevation of her fasting glucose level, this is GDM because its first recognition was during pregnancy. There is no need to perform further testing in this patient. A single elevated fasting glucose of >126 mg/dl obviates further testing. A glycohemglobin could be performed, and, if elevated, supports the likelihood of pre-existing diabetes mellitus.
The patient was begun on both dietary and insulin therapy as an outpatient. Her diet included 25 kcal/kg actual body weight divided into three meals and a bedtime snack. The diet emphasized complex carbohydrates with the avoidance of simple carbohydrates. In addition, she was instructed on self-monitoring of blood glucose, performing tests while fasting and 2 hours after each meal. The targets for therapy were a fasting value of < 95 mg/dl and values no higher than 140 mg/dl at 1 hour or no higher than 120 mg/dl at 2 hours after eating. She was started empirically on 20 U of NPH and 10 U of regular insulin administered in the morning, to be adjusted after reviewing her glucose log sheets. The patient was seen each week. Given the significant elevation of her fasting glucose level, a trial of diet only was not advisable.
The patient did well on this regimen, maintaining good control until 30 weeks gestation, when her total insulin dose was increased by 20%. At 28 weeks, the patient was instructed in daily fetal movement counting to assess fetal well-being, and at 32 weeks gestation antepartum fetal heart rate testing with nonstress tests was begun twice weekly. An ultrasound examination at 37 weeks revealed the fetus to be growing normally with an estimated weight of 7 lb, 1 oz. At 39 weeks, the patient started spontaneous labor and underwent the vaginal delivery of an 8 lb, 1 oz boy. The infant was evaluated for but did not demonstrate hypoglycemia or other morbidities.
Postpartum, the patient breastfed her infant and, with her partner, decided on a barrier method of contraception: foam and condoms. Six weeks after delivery, she returned to the clinic for an evaluation of her glucose tolerance. Her fasting plasma glucose was 128 mg/dl. She returned the next day, and a repeat fasting plasma glucose was 132 mg/dl. Given these findings, the diagnosis of diabetes mellitus was made, and a 75-g OGGT test was not needed.
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Steven G. Gabbe, MD, is a professor and chair of the Department of Obstetrics and Gynecology at the University of Washington School of Medicine in Seattle.
Copyright © 1999 American Diabetes
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