Management of Gestational Diabetes Mellitus
Begin immediately with medical nutrition therapy and self-monitoring of blood glucose, targeting fasting glucose <95 mg/dL and 1-hour postprandial <140 mg/dL (or 2-hour postprandial <120 mg/dL); if these targets are not achieved within 1-2 weeks of lifestyle modifications alone, initiate insulin as first-line pharmacologic therapy. 1
Initial Management Framework
After confirming the diagnosis of GDM, treatment starts with three simultaneous interventions 2:
- Medical nutrition therapy (MNT) through referral to a registered dietitian familiar with GDM management within the first week of diagnosis 1
- Self-monitoring of blood glucose with daily fasting checks upon waking and postprandial checks after each main meal 1
- Physical activity prescription of at least 150 minutes of moderate-intensity aerobic activity weekly, spread throughout the week 1, 3
The majority (70-85%) of women diagnosed with GDM can achieve glycemic control with lifestyle modification alone, though this proportion may be even higher using the lower International Association of the Diabetes and Pregnancy Study Groups diagnostic thresholds 2, 3.
Specific Glycemic Targets
The Fifth International Workshop-Conference on Gestational Diabetes Mellitus established the following targets 2:
- Fasting glucose <95 mg/dL (5.3 mmol/L)
- 1-hour postprandial glucose <140 mg/dL (7.8 mmol/L) OR
- 2-hour postprandial glucose <120 mg/dL (6.7 mmol/L)
Choose either 1-hour or 2-hour postprandial measurements consistently; postprandial monitoring is superior to preprandial monitoring alone and is associated with better glycemic control and lower risk of preeclampsia 1.
Medical Nutrition Therapy Specifics
The nutrition plan must meet mandatory minimum requirements 2, 1, 3:
- Minimum 175 grams of carbohydrate daily (never reduce below this threshold as it risks fetal growth compromise and maternal ketosis)
- Minimum 71 grams of protein daily
- Minimum 28 grams of fiber daily
- Emphasis on monounsaturated and polyunsaturated fats while limiting saturated fats and avoiding trans fats
Carbohydrates should be distributed across 3 small-to-moderate meals and 2-4 snacks throughout the day, with an evening snack usually necessary to prevent accelerated ketosis overnight 3. The current recommended carbohydrate amount represents approximately 35% of a 2,000-calorie diet 2.
Critical pitfall: Avoid hypocaloric diets <1,200 kcal/day, which cause ketonemia, and never restrict carbohydrates below 175g/day 3.
Pharmacologic Management Algorithm
If glycemic targets are not met within 1-2 weeks of lifestyle modifications, insulin is the preferred and recommended first-line pharmacologic agent because it does not cross the placenta to a measurable extent 1. This recommendation is based on the lack of long-term safety data for noninsulin agents 2.
The Endocrine Society explicitly recommends avoiding metformin and glyburide as first-line therapy due to their inferior outcomes and safety profiles compared to insulin 1. A meta-analysis of 11 RCTs demonstrated that metformin treatment in pregnancy does not reduce the risk of GDM in high-risk individuals 2.
Insulin dosing requires frequent titration to match changing requirements throughout pregnancy 2:
- First trimester: Often a decrease in total daily dose
- Second trimester: Rapidly increasing insulin resistance requires weekly or biweekly increases
- General principle: A smaller proportion of total daily dose should be given as basal insulin and a greater proportion as prandial insulin 2
Monitoring Strategy
Blood glucose monitoring should include 1:
- Daily fasting glucose upon waking
- Postprandial glucose after each main meal (breakfast, lunch, dinner)
- Choose consistently between 1-hour or 2-hour postprandial measurements
HbA1c has limited utility in GDM management but if used, should be measured monthly with a target <6% (42 mmol/mol) if achievable without significant hypoglycemia 1. HbA1c should NOT replace blood glucose monitoring because macrosomia results primarily from postprandial hyperglycemia, which HbA1c may not adequately detect 1.
Fetal surveillance should begin in the second and early third trimesters with ultrasound monitoring of fetal abdominal circumference repeated every 2-4 weeks 1. Consider intensifying glycemic control when fetal abdominal circumference exceeds the 75th percentile for gestational age 1.
Telehealth Considerations
A meta-analysis of 32 RCTs demonstrated that telehealth visits for GDM reduce incidences of cesarean delivery, neonatal hypoglycemia, premature rupture of membranes, macrosomia, pregnancy-induced hypertension or preeclampsia, preterm birth, neonatal asphyxia, and polyhydramnios compared with standard in-person care 2.
Delivery Timing
Delivery timing depends on glycemic control 1:
- Diet-controlled GDM meeting glycemic targets: Delivery at 39-40 weeks of gestation
- Insulin-requiring GDM or poor glycemic control: Delivery at 39 weeks of gestation
Assess for fetal macrosomia (estimated fetal weight >4,000 g) and discuss risks and benefits of prelabor cesarean delivery if estimated fetal weight exceeds 4,500 g 4.
Postpartum Management
All women with GDM must be tested for persistent diabetes or prediabetes at 4-12 weeks postpartum using a 75-g oral glucose tolerance test with non-pregnancy diagnostic criteria 1. Do NOT use HbA1c at this visit because the concentration may still be influenced by changes during pregnancy and/or peripartum blood loss 1.
Women with a history of GDM have a 50-70% risk of developing type 2 diabetes over 15-25 years and require lifelong screening for diabetes at least every 3 years 1. Continued lifestyle modifications and breastfeeding can reduce this risk 4.
Critical pitfall: Avoid continuing pregnancy-specific insulin regimens postpartum unless there is a specific indication; transition to standard diabetes management with metformin as first-line agent if lifestyle changes alone do not achieve glycemic targets within 3 months 5.