Gestational Diabetes Mellitus
Christina C. Reed and Susan Drummond
Definition
A.Gestational diabetes mellitus (GDM) is a carbohydrate intolerance with onset or recognition during pregnancy.
Incidence
A.It is estimated that up to 6% to 7% of pregnancies are complicated by diabetes mellitus (DM) and approximately 90% of these cases represent women with GDM. It usually resolves after pregnancy.
Pathogenesis
A.Insulin antagonism caused by the placental hormones leads to gestational diabetes. As greater amounts of these hormones are produced with advancing gestation, the diabetogenic effect of pregnancy becomes more pronounced, reaching significant levels in the second trimester. Women with GDM are at risk for later development of type 1 and type 2 diabetes, metabolic syndrome, and cardiovascular disease. GDM may actually be the expression of pregnancy-induced stresses on carbohydrate metabolism in the genetically predisposed patient. It is estimated that 50% to 70% of women with GDM will develop DM within approximately 15 to 25 years of the pregnancy. Some women have undiagnosed type 1 or 2 diabetes prior to pregnancy.
Predisposing Factors
A.Members of any of the following ethnic groups:
1.Hispanic American.
2.African American.
3.Native American.
4.South or East Asian.
5.Pacific Islander.
B.Maternal age older than 25 years.
C.Obesity (body mass index [BMI] >30).
D.Family history of diabetes, first-degree relatives.
E.Previous birth of a macrosomic, malformed, or stillborn baby.
F.Comorbidity: Metabolic syndrome, hypertension, polycystic ovarian syndrome, use of glucocorticoids.
G.Glycosuria at prenatal visit.
H.Gestational diabetes in a previous pregnancy.
I.Multiple gestation.
Common Complaints
A.Common complaints of hyperglycemia include polydipsia, polyuria, nocturia, fatigue, and blurred vision. However, gestational diabetes is often asymptomatic.
Other Signs and Symptoms
A.Glycosuria.
B.Fundal height measurement greater than gestational age in weeks.
C.Frequent candidal infections.
D.Rapid weight gain.
Potential Complications
A.Ketoacidosis:
1.May develop in GDM.
2.More common in insulin-dependent diabetes.
3.May develop with glucose levels as low as 200 mg/dL.
4.May be present in an undiagnosed diabetic woman receiving beta-mimetic agents (such as terbutaline) for tocolysis or steroids to enhance fetal lung maturity. Fetal mortality rate is 10% in women who come to the hospital in diabetic ketoacidosis (DKA). Glucose and ketones cross the placenta.
5.Therapy hinges on timely, aggressive volume resuscitation, insulin administration, and correction of maternal electrolyte imbalance.
B.Polyhydramnios.
C.Increased risk for neonatal morbidity such as hypoglycemia, hyperbilirubinemia, polycythemia, respiratory distress caused by delayed lung maturity, and/or traumatic birth injury related to shoulder dystocia, which is associated with macrosomia.
D.Increased risk for stillbirth—risk is related primarily to poor glycemic control.
E.Preeclampsia.
F.Operative delivery.
G.Fetal organomegaly.
H.Long-term sequelae for the offspring: Abnormal glucose tolerance, metabolic syndrome, and obesity.
Subjective Data
A.Review previous pregnancy history for two or more spontaneous abortions, previous stillbirths, or unexplained neonatal deaths.
B.Review birth weight (macrosomia) and gestational age of previous children.
C.Review previous pregnancy history for polyhydramnios and/or congenital anomalies.
D.Review the patient’s history for a predisposition to infections, especially urinary tract infections (UTIs) and candidal vaginitis, and for family history of diabetes.
E.Review previous pregnancy history for gestational diabetes, diet restrictions, and need for insulin therapy.
Physical Examination
A.Check blood pressure (BP), pulse, and weight.
B.Inspect: Perform speculum exam to rule out sexually transmitted infections (STIs), bacterial vaginosis, and candidal vaginitis, if indicated.
C.Palpate: Check the patient’s fundal height each visit after 20 weeks.
D.Auscultate fetal heart tones after 10 to 12 weeks’ gestation.
Screening/Diagnostic Tests
Women who have risk factors for type 2 diabetes should be screened at the initial prenatal visit.
A.Perform one-step
2-hour 75 g (fasting) oral glucose tolerance test (OGTT) or two-step
1-hour 50 g (nonfasting) followed by a 3-hour 100 g (fasting) OGTT for positive results.
B.Blood glucose measurements (fasting blood sugar [FBS] and 2-hour postprandial blood glucose values).
C.HgbA1c.
D.Urine dipstick for glucose: Early glycosuria needs further. evaluation (i.e., HgbA1c, urine culture, random glucose finger stick
).
E.Ultrasonography if fetal size is greater than average for gestational date to rule out twins, congenital anomaly such as atresia, and polyhydramnios.
Differential Diagnoses
A.Gestational diabetes:
1.A1: Diet-controlled gestational diabetes (A1 GDM).
2.A2: Insulin-treated gestational diabetes (A2 GDM).
Plan
A.General interventions:
1.The American Diabetes Association (ADA) recommends that all pregnant women be screened:
a.Diabetes mellitus screen (DMS): Two-step
1-hour 50 g (nonfasting) oral glucose challenge test (OGCT) followed by a 3-hour 100 g OGTT for positive results:
i.Administer 50 g oral glucose load (fasting not required; however, no food/nonwater
beverages for 2 hours prior to the test).
ii.Draw blood for glucose assessment 1 hour after glucose load is given.
iii.Typically performed between 24 and 28 weeks’ gestation; performed earlier if the patient has glycosuria, predisposing risk factors, or advanced maternal age (AMA), or if fetal size is greater than average for gestational date by fundal height measurement.
iv.Abnormal result of the 1-hour 50 g OGCT is a glucose level of 130 to 140 mg/dL (use your institutional limits).
v.If the results of the 1-hour 50 g OGCT is ≥200 mg/dL, the patient skips the 3-hour 100 g OGTT and begins dietary modifications and glucose evaluation for insulin needs.
vi.Follow up all abnormal 1-hour OGCT with a 3-hour OGTT.
b.3-hour OGTT:
i.Draw fasting blood glucose first.
ii.Administer 100 g glucose load.
iii.Draw blood for glucose assessment after 1 hour, 2 hours, and 3 hours from the time the glucose load is given.
iv.Plasma or serum glucose results (Carpenter/-Coustan criteria or use institutional limits):
•Fasting = 95 mg/dL.
•1 hour = 180 mg/dL.
•2 hours = 155 mg/dL.
•3 hours = 140 mg/dL.
v.If two or more values of 3-hour GTT are elevated:
•Refer the patient for nutritional counseling for dietary modifications.
•Glucose evaluation for insulin needs. Daily blood sugar log to record fasting and 2-hour postprandial blood glucose measurements.
c.One-step
2-hour 75 mg (fasting) OGTT may be performed instead of the two-step
approach.
2.Antepartum testing:
a.For women with well-controlled A1 GDM on nutritional therapy and no other pregnancy complication, there is no national consensus with respect to criteria for initiation and timing of testing. Options include weekly or twice weekly nonstress tests (NSTs) and biophysical profiles (BPPs) beginning at 32 weeks. Use institutional guidelines.
b.Women with insulin-dependent diabetes or using oral hyperglycemic agents, or with poorly controlled A2 GDM, need twice weekly NSTs and BPPs beginning at 32 weeks or sooner depending on if other pregnancy complications exist. If a patient’s diabetes is poorly controlled, consider fetal assessment earlier and more frequently.
3.Serial ultrasonography:
a.Evaluate fetal growth, estimate fetal weight, and detect polyhydramnios and malformations.
b.There is no national consensus with respect to criteria for initiation and timing to assess growth; however, practice agrees on one single ultrasound (US) at 36 weeks or starting USs at 28 weeks and repeating them thereafter, every 4 weeks (28, 32, 36 weeks).
c.Macrosomia is a leading risk factor for shoulder dystocia at vaginal delivery and cephalopelvic disproportion. Women with GDM should be counseled regarding the option of a scheduled cesarean delivery when the fetus is more than or equal to 4,500 g.
4.Neonate evaluation:
a.Monitor neonate carefully for hypoglycemia, especially if the patient has a history of insulin-dependent diabetes.
5.Postpartum:
a.Testing:
i.Two-hour GTT between 6 and 12 weeks postpartum (fasting):
•Administer 75 g glucose load.
•Draw blood for glucose assessment at 2 hours after the glucose load is given.
•Results ≥200: Diabetes management is needed.
ii.Consider serial measurement of total cholesterol, low-density lipoprotein, high-density lipoprotein, and triglycerides.
b.Contraception:
i.Low-dose oral contraceptives (OCs) may be used in women with GDM who do not have other risk factors.
ii.Rate of subsequent diabetes in OC users is not significantly different from those who do not use OCs.
B.Patient teaching: GDM requires intensive patient and family education to maintain glucose targets to help reduce perinatal complications:
1.Exercise:
a.If the patient had an active lifestyle prior to pregnancy, encourage her to continue a program of exercise approved for pregnancy such as walking or swimming for 20 minutes per day.
b.Upper extremity exercise and walking in previously sedentary women with GDM may improve glycemic control.
2.Instruct the patient in self-monitoring blood glucose and encourage them to record each blood glucose measurement:
a.Have her take measurements fasting and 2 hours postprandially every day and record the measurements. Postprandial blood sugar values are recommended over preprandial values because of better glycemic control and better maternal/fetal outcomes. FBS should be less than 95 mg/dL. The 1-hour postprandial values should be less than 140 mg/L and the 2-hour postprandial values should be less than 120 mg/L. The HgbA1c goal is less than 6%. Nighttime levels should not decrease lower than 60 mg/dL.
b.If the patient is taking multiple doses of insulin, she may need to take measurements more frequently.
3. 
See Section III: Patient Teaching Guide Gestational Diabetes Mellitus.
C.Dietary management: Place the patient on a diet that is prescribed for preexisting diabetes in pregnancy, such as the ADA diet, in the following amounts:
1.Current weight less than 80% ideal body weight (IBW): 35 to 40 kcal/kg/d.
2.Current weight 80% to 120% IBW: 30 kcal/kg/d.
3.Current weight 120% to 150% IBW: 22 to 25 kcal/kg/d.
4.Current weight more than 150% IBW: 12 to 14 kcal/kg/d (minimum of 1,800 cal/d to prevent ketosis).
5.Dietary consumption:
a.Total calories: 1,800–2,500 kcal/d based on IBW.
b.Trimester specific recommendations:
i.First trimester no increase in calories.
ii.Second trimester 340 kcal/d increase above prepregnancy levels.
iii.Third trimester 452 kcal/d increase above prepregnancy levels.
c.Nutrition distribution:
i.Carbohydrate 40% to 50% (minimum 175 g/d).
ii.Protein 20% (71 g/d).
iii.Fat 30% to 40%.
iv.Fiber 28 g/d.
D.Pharmaceutical therapy:
1.Insulin therapy is the drug of choice if medical nutritional therapy does not consistently maintain fasting glucose levels of less than 95 mg/dL. One-hour postprandial values should be less than 140 mg/dL. Two-hour postprandial values should be less than 120 mg/dL (see Figure 16.1).