Basics
Description
- Gestational diabetes mellitus (GDM) is the new onset of diabetes mellitus (DM) or impaired glucose tolerance during pregnancy.
- Maternity care providers should distinguish between preexisting but undiagnosed type 2 diabetes mellitus (T2DM) and GDM.
- GDM that persists beyond pregnancy should be reclassified as T2DM.
- A1 GDM refers to GDM controlled by lifestyle alone.
- A2 GDM refers to pharmacologically managed GDM and implies suboptimal glycemic control.
Epidemiology
Prevalence
- 6-7% of pregnancies in United States may be as high as 18% with more recently proposed diagnostic criteria (see "Diagnostic Tests"� below).
- Highest among Hispanic, African American, Native American, Asian, and Pacific Islander women
- Varies according to local prevalence of T2DM
- Increasing globally
Etiology and Pathophysiology
- The etiology of GDM is poorly understood.
- During pregnancy, the placenta produces several hormones that can cause or exacerbate insulin resistance in susceptible individuals.
Genetics
- Incompletely understood
- Strong family association
- Polygenic risk plus environmental factors
Risk Factors
- History of GDM in previous gestation
- History of impaired glucose metabolism (A1c ≥5.7%, impaired glucose tolerance, or impaired fasting glucose)
- Obesity (body mass index [BMI] ≥30 kg/m2)
- Overweight (BMI ≥25 kg/m2) with additional risk factors
- Physical inactivity
- Diabetes in 1st-degree relative
- High-risk ethnicity (see "Prevalence"� above)
- Previous delivery of baby weighing >9 lb
- Hypertension
- HDL cholesterol <35 mg/dL
- Triglyceride level >250 mg/dL
- Polycystic ovary syndrome
General Prevention
- Weight loss or maintain healthy weight before pregnancy.
- Regular exercise including both aerobic and resistance training (based on data from observational studies).
Commonly Associated Conditions
- Prediabetes
- Impaired fasting glucose
- Impaired glucose tolerance
- A1c 5.7-6.4%
- Hypertensive disorders of pregnancy
- Gestational hypertension
- Preeclampsia
Diagnosis
History
- Usually asymptomatic
- Ask all pregnant women about risk factors (see above) at first prenatal visit.
Physical Exam
- May be normal
- Overweight, obesity common
- Acanthosis nigricans suggests T2DM.
- Excessive weight gain may occur during pregnancy complicated by GDM.
- Excessive fundal height may indicate fetal macrosomia.
Differential Diagnosis
- Preexisting/pregestational T2DM
- Stress hyperglycemia
Diagnostic Tests & Interpretation
Initial Tests (lab, imaging)
- Screen for undiagnosed T2DM at the first prenatal visit in women with risk factors (see above) using standard criteria (1)[A]:
- A1c ≥6.5%
- Fasting serum glucose ≥126 mg/dL
- 2-hour postprandial glucose ≥200 mg/dL
- Screen for GDM at 24-28 weeks of gestation in pregnant women not previously known to have diabetes. Both two-step and one-step methods of screening are acceptable (2).
- Standard two-step screening for GDM endorsed by the American College of Obstetricians and Gynecologists (ACOG) (2,3)[A]:
- Step 1: 1-hour nonfasting 50-g glucose load test (GLT); if 1-hour plasma glucose meets or exceeds threshold then proceed to step 2; threshold may be set at 140 mg/dL, 135 mg/dL, or 130 mg/dL (American Diabetes Association endorses 140 mg/dL).
- Step 2: 3-hour fasting 100-g oral glucose tolerance test (OGTT); the diagnosis of GDM is made when ≥2 glucose values are met or exceeded using either of two accepted sets of criteria:
- Carpenter/Coustan
- Fasting ≥95 mg/dL
- 1 hour ≥180 mg/dL
- 2 hour ≥155 mg/dL
- 3 hour ≥140 mg/dL
- National Diabetes Data Group
- Fasting ≥105 mg/dL
- 1 hour ≥190 mg/dL
- 2 hour ≥165 mg/dL
- 3 hour ≥145 mg/dL
- Alternative one-step screening for GDM (1)[A]
- 2-hour fasting 75-g OGTT; the diagnosis of GDM is made when any of the following glucose values are met or exceeded:
- Fasting ≥92 mg/dL
- 1 hour ≥180 mg/dL
- 2 hour ≥153 mg/dL
- The use of lower thresholds for any test (1-hour GLT, 3-hour OGTT, or one-step vs. two-step screening) is more sensitive and will result in a greater number of women being diagnosed with GDM. However, at present, the clinical benefit of heightened sensitivity is uncertain.
Follow-up tests & special considerations
Screening for GDM may be considered optional for women at very low risk for GDM (i.e., non-Hispanic White, <25 years of age, BMI <25 kg/m2, no history of GDM or glucose intolerance, and no 1st-degree relative with diabetes); this is only 10% of the U.S. obstetric population. �
Diagnostic Procedures/Other
- Ultrasound at 37-39 weeks of gestation for estimated fetal weight (evaluation for fetal macrosomia, see "Surger/Other Procedures"� below)
- Antenatal testing, typically some combination of the following performed twice weekly beginning in 3rd trimester for A2 GDM, although current evidence does not support a particular protocol.
- Fetal nonstress test (NST; reactive with ≥2 accelerations in 20-40 minutes)
- Amniotic fluid index (AFI; normal >5 cm)
- Biophysical profile (BPP; presence or absence of five variables; score of ≥8 out of 10 including AFI >5 cm is normal)
- Modified BPP (NST plus AFI, equivalent to BPP if NST reactive and AFI >5 cm)
Treatment
General Measures
- Treatment benefits both mother and fetus (1,2,4)[A].
- Dietary therapy for all women with GDM
- Add medication when necessary for glycemic control.
- Oral medications not FDA-approved for GDM but equivalent to insulin in efficacy
Medication
First Line
- Metformin 500-1,000 mg by mouth b.i.d. with meals (2,5)[A]
- Glyburide 2.5-10 mg by mouth b.i.d. (2)[A]
- Do not use in patients who have sulfa allergy.
- Insulin 0.7-1 unit/kg/day in divided doses; usually given half as intermediate-acting (either NPH or detemir) and half as rapid-acting (either lispro or aspart) with meals (1,2)[A]:
- Insulin NPH 0.35-0.5 units/kg/day SUBQ divided b.i.d. or t.i.d. or
- Insulin detemir 0.35-0.5 units/kg/day SUBQ daily or divided b.i.d. plus
- Insulin lispro or insulin aspart 0.35-0.5 units/kg/day SUBQ divided t.i.d. with meals
Second Line
Combination therapy (usually metformin + insulin) �
Issues for Referral
- Nutrition counseling by registered dietician
- Diabetic education if available
- Consider perinatology consult for
- Poor glycemic control
- Maternal comorbidities
- Other high risk or management uncertainty
Additional Therapies
Exercise probably beneficial and safe but not well studied in GDM. �
Surgery/Other Procedures
- Consider scheduled cesarean section in GDM if estimated fetal weight ≥4,500 g (2)[C].
- Evidence is insufficient to recommend delivery at any particular gestational age.
- Women with GDM with good glycemic control by diet or medication and no other complications usually can be managed expectantly until ≥39 weeks of gestation (2)[C].
- Some obstetricians recommend delivery between 39 and 40 weeks of gestation as with well-controlled, pregestational diabetes.
- Others recommend induction at 39 weeks in A2 GDM and at 41 weeks in A1 GDM.
Inpatient Considerations
Admission Criteria/Initial Stabilization
- Periodic glucose monitoring during labor
- Intrapartum glycemic control (ideally 70-110 mg/dL) is important for minimizing risk of neonatal hypoglycemia.
IV Fluids
- Normal saline (NS) or lactated Ringer (LR) with or without 5% dextrose (D5) depending on glucose levels, stage of labor, and need for insulin to maintain glycemic control during labor
- ACOG protocol
- NS at start of labor
- D5NS at 100-150 mL/hour if glucose <70 mg/dL or during active labor
- Regular insulin at 1.25 units/hour (10 units per 1,000 mL D5NS at 125 mL/hour) if glucose >100 mg/dL
Nursing
- Resume normal diet and discontinue pharmacotherapy postpartum.
- Monitor glucose for 24-72 hours postpartum to confirm normalization.
- Breastfeeding helps with maternal glucose metabolism and should be encouraged.
Discharge Criteria
Euglycemic and otherwise stable �
Ongoing Care
Follow-up Recommendations
- Routine postpartum follow-up unless pharmacotherapy is continued.
- GDM is associated with a nearly 2-fold risk for postpartum depression.
- Screen for T2DM at 6-12 weeks postpartum using 2-hour 75-g OGTT:
- Glucose 140-199 mg/dL indicates impaired glucose tolerance (prediabetes).
- Glucose ≥200 mg/dL indicates T2DM.
- Continue screening women who have had GDM for T2DM using standard criteria every 3 years for life.
Patient Monitoring
During pregnancy, monitor fasting glucose at either 1-hour or 2-hour postprandial glucose levels (up to 4 times daily) until control is established; intensify therapy whenever the following targets are not consistently met: �
- Fasting ≤95 mg/dL
- 1-hour postmeal ≤140 mg/dL
- 2-hour postmeal ≤120 mg/dL
Diet
- Personalized nutrition plan based on BMI
- Limit carbohydrates from 33 to 40% of calories.
- Complex versus simple carbohydrates preferred
- 3 meals plus 2 or 3 snacks per day
Patient Education
Women with GDM should receive education about potential complications (see below), the importance of glycemic control during pregnancy, their future risk of T2DM (see "Prognosis"� below), and ways to reduce that risk (see "General Prevention"� above). �
Prognosis
- Risk of recurrent GDM in subsequent pregnancy is approximately 41%.
- Women who have had GDM are at 7-fold increased risk for developing T2DM.
- 1/3 will have diabetes or impaired glucose metabolism at postpartum testing.
- 15-50% will develop T2DM later in life.
Complications
- Maternal
- Gestational hypertension
- Preeclampsia
- Cesarean delivery
- Subsequent development of T2DM
- Fetal
- Macrosomia
- Shoulder dystocia
- Birth trauma
- Neonatal hypoglycemia
- Neonatal hyperbilirubinemia
References
1.American Diabetes Association. Standards of medical care in diabetes-2014. Diabetes Care. 2014;37(Suppl 1):S14-S80. �
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2.Committee on Practice Bulletins-Obstetrics. Practice Bulletin No. 137: Gestational diabetes mellitus. Obstet Gynecol. 2013;122(2 Pt 1):406-416. �
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3.Donovan �L, Hartling �L, Muise �M, et al. Screening tests for gestational diabetes: a systematic review for the U.S. Preventive Services Task Force. Ann Intern Med. 2013;159(2):115-122. �
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4.Hartling �L, Dryden �DM, Guthrie �A, et al. Benefits and harms of treating gestational diabetes mellitus: a systematic review and meta-analysis for the U.S. Preventive Services Task Force and the National Institutes of Health Office of Medical Applications of Research. Ann Intern Med. 2013;159(2):123-129. �
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5.Gui �J, Liu �Q, Feng �L. Metformin vs insulin in the management of gestational diabetes: a meta-analysis. PLoS One. 2013;8(5):e64585. �
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Additional Reading
- Perinatology.com. Gestational diabetes: calculation of caloric requirements and initial insulin dose. Available at http://www.perinatology.com/calulators/GDM.htm
See Also
Diabetes Mellitus, Type 2 �
Codes
ICD09
- 648.80 Abnormal glucose tolerance of mother, unspecified as to episode of care or not applicable
- 648.83 Abnormal glucose tolerance of mother, antepartum condition or complication
- V12.21 Personal history of gestational diabetes
- 648.81 Abnormal glucose tolerance of mother, delivered, with or without mention of antepartum condition
- 648.82 Abnormal glucose tolerance of mother, delivered, with mention of postpartum complication
- 648.84 Abnormal glucose tolerance of mother, postpartum condition or complication
ICD10
- O24.429 Gestational diabetes mellitus in childbirth, unsp control
- O24.420 Gestational diabetes mellitus in childbirth, diet controlled
- Z86.32 Personal history of gestational diabetes
- O24.424 Gestational diabetes in childbirth, insulin controlled
SNOMED
- 11687002 Gestational diabetes mellitus (disorder)
- 75022004 Gestational diabetes mellitus, class A1 (disorder)
- 472971004 History of gestational diabetes mellitus (situation)
- 46894009 Gestational diabetes mellitus, class A2 (disorder)
Clinical Pearls
- Screen for undiagnosed T2DM at the first prenatal visit in women with risk factors.
- Screen for GDM at 24-28 weeks of gestation in pregnant women not previously known to have diabetes. Both one-step and two-step methods of screening are acceptable.
- Treat all women diagnosed with GDM using dietary therapy and, if necessary, medication. Metformin, glyburide, and insulin are first-line options if pharmacotherapy is needed.
- Screen women who have had GDM for T2DM 6-12 weeks postpartum and every 3 years thereafter.