Gestational Diabetes in Primary Care

Paul Hicks, MD

Delivery

Labor is a relatively uncomplicated process, in terms of diabetes care. For the woman whose diabetes is diet controlled, FSBS are done every 2 to 4 hours during labor; for the woman who requires insulin, FSBS are performed every 1 to 2 hours. An intravenous insulin drip is begun if FSBS is > 120 to 140 mg/dL ( Table 5 ).

Maternal complications that may arise intrapartum include PIH and pre-eclampsia, hyperglycemia and hypoglycemia, and arrested labor from shoulder dystocia. PIH and pre-eclampsia are much more common in women with pregestational diabetes, especially those women who have peripheral vascular disease. However, these can also occur in women with GDM, often in association with polyhydramnios. Care of the woman with GDM with pre-eclampsia is no different than care of the nondiabetic patient. Shoulder dystocia occurs in 2% of all pregnancies and in 11% to 14% of pregnancies complicated by GDM.^[49,50] There are 2 reasons for this difference in incidence rates: First, the incidence of macrosomia is greater. Second, in GDM there is a significantly increased trunk-to-head ratio compared with nonaffected infants of similar weight.^[51] Infants affected by GDM have a predictable appearance of large trunks and shoulders relative to their heads. This effectively impacts them into the pelvis, making passage much more difficult. The risk increases precipitously as fetal weight increases. For infants weighing ≤ 3999 g, the incidence of shoulder dystocia is 9%. For infants weighing 4000 to 4499 g, the risk increases to 14% -- hence, the recommendation for induction at that time. In infants weighing ≥ 4500 g, the incidence of shoulder dystocia for vaginal birth is a startling 38%, making cesarean delivery the preferred route.^[49] Of note, however, one third of cases of shoulder dystocia occur in infants weighing < 4000 g.^[50] As such, it is important for every provider to be able to manage the delivery of these infants.

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Table 1. Composition of Study Population by Race/Ethnicity With 50-g Oral Glucose Screening Test and 3-Hour Glucose Tolerance Test Results
Race/Ethnicity	N	Third-Trimester GST Result* (mg/dL)	Third-Trimester GST Result > 140 mg/dL	GDM Diagnosed in Patients With GST > 140 mg/dL	Prevalence of GDM Diagnosed in Third Trimester
White	654 (71%)	123.2±28.4	27.4%	17.3%	6.0%
Hispanic	512 (56%)	123.2±28.3	26.8%	18.2%	6.3%
Non-Hispanic	142 (15%)	123.5±28.5	29.6%	14.3%	4.9%
Black	120 (13%)	116.4±31.6	17.5%	42.9%	7.5%
Filipino	83 (9%)	127.6±26.3	31.3%	11.5%	3.6%
Asian^†	64 (7%)	134.7±25.0	40.6%	11.5%	4.7%

GST = to-g oral glucose screening test
*Mean + SD.
^†Asian includes subjects of Chinese, Japanese, Korean, Vietnamese, Thai, Cambodian, and Laotian ethnicity.; Reprinted with permission from Nahum and Huffaker.^[14]

Table 2. Recommended Race-Specific Glucose Screening Test Thresholds for Initiating 3-Hour Glucose Tolerance Testing, With Expected Yields of Positive Results by Race
	Blacks	Whites	Filipinos	Asians
Recommended upper limit threshold for normalcy of GST result (mg/dL)*	130	140	145	150
Expected proportion of gravidas exceeding threshold limit	24.2%	27.4%	27.7%	23.4%
Expected percentage of gravidas diagnosed with GDM in third trimester	7.5-8.3%	4.7%	3.6%	3.1%

*Plasma glucose oxidase values; Reprinted with permission from Nahum and Huffaker.^[14]

Table 3. Detection of Gestational Diabetes*
100-g oral glucose tolerance test	O'Sullivan Criteria	Carpenter Conversion
Fasting	105	95
1-hour	190	180
2-hour	165	155
3-hour	145	140

*Diagnosis of gestational diabetes is made when any 2 values are met or exceeded.; Reprinted with permission from American College of Obstetricians and Gynecologists.^[1]

Table 4. Caloric Restrictions in Obese and Nonobese Women With GDM
Distribution of Calories in a Diabetic Diet
Breakfast = 20% total kcal/day
Lunch = 25%
Supper = 25%
3 snacks, after each meal = 5% each
1 snack before bed = 15%

Adapted from Langer and Hod.^[29]

Table 5. Low-Dosage Constant Insulin Infusion for the Intrapartum Period*
Blood Glucose (mg/100 mL)	Insulin Dosage (U/hr)	Fluids (125 mL/hr)
< 100	0	Dextrose/Lactated Ringer's
100-140	1.0	Dextrose/Lactated Ringer's
141-180	1.5	Normal saline
181-220	2.0	Normal saline
> 220	2.5	Normal saline

*Dilution is 25 U of regular insulin in 250 mL of normal saline with 25 mL flushed through line administered intravenously. A finger-stick glucose test is performed every 1-2 hours. The insulin pump and intravenous solution are adjusted accordingly.; Adapted from Hollingsworth and Moore.^[62]

Table 6. Postpartum Evaluation for Carbohydrate Intolerance
Plasma glucose level*(mg/dL) in
Time Tested	No Diabetes	Impaired Glucose Tolerance	Diabetes Mellitus
Fasting	< 110	>/= 110 and < 126	>/= 126
2 h	< 140	140-199	>/= 200

*Values are based on a 2-h, 75-g oral glucose tolerance test.; Reprinted with permission from the American Diabetes Association.^[16]

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Gestational Diabetes in Primary Care

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