Case Study: A 34-Year-Old Woman in Her Second Pregnancy at 24 Weeks Gestation

CLINICAL DIABETES
VOL. 17 NO. 3 1999

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CASE STUDIES

Steven G. Gabbe, MD

Presentation
A 34-year-old Hispanic-American woman who is in her second pregnancy and has had one live birth and no abortions is seen for prenatal care at 24 weeks gestation. Her weight is 220 lb, and her blood pressure is 130/80 mmHg. Uterine size is appropriate for gestational age. The patient's past obstetric history includes the spontaneous vaginal delivery of a 9 lb, 8 oz. male infant at 40 weeks gestation, 8 years ago in Mexico. The patient reports that the child is doing well. Her family history reveals that her mother has type 2 diabetes mellitus. A urine dipstick shows 3+ glycosuria and negative ketones.

Questions

1. What tests should be done to evaluate the patient's glucose tolerance?
2. How is the diagnosis of gestational diabetes mellitus (GDM) established?
3. What would be the best treatment and follow-up strategy?

Commentary
This patient presents with several risk factors for GDM, defined as carbohydrate intolerance of varying degrees of severity with onset or first recognition during pregnancy, regardless of whether insulin is used for treatment or the condition persists after pregnancy. She is over 30 years of age, from an ethnic group at increased risk for type 2 diabetes mellitus, is obese, and has a first-degree relative with type 2 diabetes.

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.

Clinical Pearls

1. When patients present with significant risk factors for GDM, early screening for GDM, before 20 weeks gestation, might be undertaken.

2. The finding of glycosuria should prompt a random capillary glucose performed immediately and a follow-up fasting venous plasma glucose.

3. Given an elevated fasting venous plasma glucose, such patients should be started immediately on diet and insulin therapy and followed with self-monitoring of blood glucose using the criteria recommended by the Fourth International Workshop-Conference on Gestational Diabetes Mellitus.

4. Patients treated with not only diet but also insulin are at increased risk for an intrauterine fetal death, and for that reason, antepartum fetal testing with nonstress tests should be performed.

5. For such patients who do not enter spontaneous labor, induction of labor at 39 weeks is appropriate.

6. Postpartum, this patient was found to have an elevated fasting plasma glucose and the diagnosis of diabetes mellitus was made. That diabetes persisted after delivery is not surprising given that the diagnosis of GDM was made relatively early in pregnancy, that the fasting plasma glucose exceeded 140 mg/dl, and that the patient was obese.

SUGGESTED READINGS

Carpenter MW, Coustan DR: Criteria for screening tests for gestational diabetes. Am J Obstet Gynecol 144:768–73, 1982.

Expert Committee on the Diagnosis and Classification of Diabetes Mellitus: Report of the expert committee on the diagnosis and classification of diabetes mellitus. Diabetes Care 20:1182–97, 1997.

Gabbe SG, Mestman JH, Freeman RK, Anderson GV, Lowensohn RI: Management and outcome of Class A diabetes mellitus. Am J Obstet Gynecol 127:465–69, 1977.

Gregory KD, Kjos SL, Peters RK: Cost on non-insulin-dependent diabetes in women with a history of gestational diabetes: implication for prevention. Obstet Gynecol 81:182–86, 1993.

Kjos SL, Buchanan TA, Greenspoon JS, Montoro M, Bernstein GS, Mestman JH: Gestational diabetes mellitus: the prevalence of glucose intolerance and diabetes mellitus in the first two months postpartum. Am J Obstet Gynecol 163:93–98, 1990.

Metzger BE, Coustan DR, The Organizing Committee: Proceedings of the Fourth International Workshop-Conference on Gestational Diabetes Mellitus. Diabetes Care 21(Suppl. 2):B161–67, 1998.

American Diabetes Association: Position statement: Standards of medical care for patients with diabetes mellitus. Diabetes Care 22(Suppl. 1): S32–41, 1999.

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.

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