High-Risk Gestational Diabetes Mellitus: Risk Factors and Management
Identifying Very High-Risk Patients
Women at very high risk for GDM should be screened for diabetes as soon as possible after confirmation of pregnancy, not waiting until 24-28 weeks. 1
The criteria defining very high risk include:
- Severe obesity 1
- Prior history of GDM or delivery of large-for-gestational-age infant 1
- Presence of glycosuria 1
- Diagnosis of polycystic ovary syndrome (PCOS) 1
- Strong family history of type 2 diabetes 1
Additional independent risk factors that increase GDM risk include:
- Age ≥30 years (risk increases with age, particularly when combined with other factors) 2
- Pre-pregnancy BMI ≥30 (risk increases linearly with BMI) 2
- High-risk ethnicity (Native American, African American, Latino, Asian American, Pacific Islander) 1, 3
Screening Strategy for High-Risk Patients
For very high-risk women, perform standard diagnostic testing (fasting plasma glucose or OGTT) at the first prenatal visit. 1 This early screening identifies preexisting undiagnosed type 2 diabetes or early-onset GDM, allowing prompt implementation of glucose control measures. 4
If initial screening is normal in high-risk women, repeat GDM testing at 24-28 weeks of gestation using either a two-step approach (50-g glucose challenge test followed by 100-g OGTT if abnormal) or one-step approach (diagnostic 100-g OGTT). 1 The one-step approach may be preferred in clinics with high prevalence of GDM. 1
For the 100-g OGTT, GDM is diagnosed when at least two of the following plasma glucose values are met:
- Fasting ≥95 mg/dL
- 1-hour ≥180 mg/dL
- 2-hour ≥155 mg/dL
- 3-hour ≥140 mg/dL 1
Management During Pregnancy
Treatment should begin with medical nutrition therapy (individualized meal plan with minimum 175g carbohydrates, 71g protein, 28g fiber daily, distributed into three small-to-moderate meals and 2-4 snacks), moderate physical activity (20-50 minutes per day, 2-7 days per week), and daily glucose monitoring. 5
Glycemic targets are: fasting <95 mg/dL, 1-hour postprandial <140 mg/dL, and 2-hour postprandial <120 mg/dL. 5
Approximately 70-85% of women with GDM can achieve control with lifestyle modifications alone, though obese women frequently require pharmacotherapy. 1, 5
When glycemic targets are not met with lifestyle modifications, insulin is the recommended first-line pharmacological treatment. 5 Insulin does not cross the placenta in measurable amounts, making it safer than oral agents. 5 The initial total daily insulin dose is calculated as 0.7-1.0 units/kg of current weight, with 40% given as basal insulin (NPH or long-acting analogs) and 60% as prandial insulin (regular or rapid-acting analogs). 5
Metformin and glyburide are not recommended as first-line treatments due to placental transfer and lack of long-term safety data. 5
Postpartum Management and Long-Term Follow-Up
Women with GDM have a 50-60% lifetime risk of developing type 2 diabetes, with approximately 20% at 10 years, increasing linearly over time. 6 This represents a 10-fold increased risk compared to women without GDM. 6
Screen for persistent diabetes or prediabetes at 6-12 weeks postpartum using a 75-g OGTT with nonpregnant criteria. 1, 6
Continue screening every 1-3 years thereafter using annual A1C, annual fasting plasma glucose, or triennial 75-g OGTT. 1, 6
Prevention Strategies for Future Diabetes
Intensive lifestyle intervention (targeting 5-10% weight loss and ≥150 minutes/week of moderate physical activity) and metformin are both effective in preventing progression to diabetes in women with prediabetes and history of GDM, with only 5-6 individuals needing treatment to prevent one case of diabetes over 3 years. 1, 6
Breastfeeding reduces the risk of developing type 2 diabetes in mothers with previous GDM and should be strongly encouraged. 1, 6
Healthy eating patterns significantly lower subsequent diabetes risk, with adjustments for BMI only moderately attenuating this association. 1, 6
Important Caveats
Women with GDM in two pregnancies have a 4.35 to 15.8-fold increased risk compared to a single GDM pregnancy. 6 Development of type 2 diabetes increases by 18% per unit of BMI increase from prepregnancy BMI. 6
For contraception, progestin-only agents (norethindrone, depo-medroxyprogesterone) should be used with caution during breastfeeding in Latino populations, as they are associated with a 2-3 fold increase in diabetes risk. 1 Combination oral contraceptives with lowest doses can be started 6-8 weeks postpartum if breastfeeding. 1