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Gestational Diabetes Mellitus

Basics

Description

- 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"пїЅ above) - Previous delivery of baby weighing >9 lb - Hypertension - HDL cholesterol <35 mg/dL - Triglyceride level >250 mg/dL - Polycystic ovary syndrome

- Nutrition counseling by registered dietician - Diabetic education if available - Consider perinatology consult for - Poor glycemic control - Maternal comorbidities - Other high risk or management uncertainty

  • 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"пїЅ 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 factorsPhysical inactivityDiabetes in 1st-degree relativeHigh-risk ethnicity (see "Prevalence"пїЅ above)Previous delivery of baby weighing >9 lbHypertensionHDL cholesterol <35 mg/dLTriglyceride level >250 mg/dLPolycystic 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

  • PrediabetesImpaired fasting glucoseImpaired glucose toleranceA1c 5.7-6.4%
  • Hypertensive disorders of pregnancyGestational hypertensionPreeclampsia

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/dL2-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/CoustanFasting ≥95 mg/dL1 hour ≥180 mg/dL2 hour ≥155 mg/dL3 hour ≥140 mg/dLNational Diabetes Data GroupFasting ≥105 mg/dL1 hour ≥190 mg/dL2 hour ≥165 mg/dL3 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/dL1 hour ≥180 mg/dL2 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. пїЅ

Diagnostic Procedures/Other

  • Ultrasound at 37-39 weeks of gestation for estimated fetal weight (evaluation for fetal macrosomia, see "Surger/Other Procedures"пїЅ 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. orInsulin detemir 0.35-0.5 units/kg/day SUBQ daily or divided b.i.d. plusInsulin 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) пїЅ

Issues for Referral

  • Nutrition counseling by registered dietician
  • Diabetic education if available
  • Consider perinatology consult forPoor glycemic controlMaternal comorbiditiesOther high risk or management uncertainty

Additional Therapies

Exercise probably beneficial and safe but not well studied in GDM. пїЅ

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 protocolNS at start of laborD5NS at 100-150 mL/hour if glucose <70 mg/dL or during active laborRegular 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 пїЅ

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: пїЅ

  • 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"пїЅ below), and ways to reduce that risk (see "General Prevention"пїЅ above). пїЅ

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

  • MaternalGestational hypertensionPreeclampsiaCesarean deliverySubsequent development of T2DM
  • FetalMacrosomiaShoulder dystociaBirth traumaNeonatal hypoglycemiaNeonatal hyperbilirubinemia

References

1.American Diabetes Association. Standards of medical care in diabetes-2014. Diabetes Care. 2014;37(Suppl 1):S14-S80. пїЅ

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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. пїЅ

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3.Donovan пїЅL, Hartling пїЅL, Muise пїЅM, 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. пїЅ

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4.Hartling пїЅL, Dryden пїЅDM, Guthrie пїЅA, 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. пїЅ

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5.Gui пїЅJ, Liu пїЅQ, Feng пїЅL. Metformin vs insulin in the management of gestational diabetes: a meta-analysis. PLoS One. 2013;8(5):e64585. пїЅ

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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 пїЅ

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.