Management of Gestational Diabetes Mellitus
Begin immediately with medical nutrition therapy and self-monitoring of blood glucose upon diagnosis, then add insulin as first-line pharmacologic therapy if glycemic targets are not met within 1–2 weeks. 1
Initial Management: Lifestyle Modifications
Medical Nutrition Therapy
Refer to a registered dietitian nutritionist within the first week of diagnosis to develop an individualized nutrition plan that provides adequate calories while achieving glycemic control. 1
Prescribe a minimum of 175 g carbohydrate daily, 71 g protein daily, and 28 g fiber daily. 1, 2, 3
Distribute carbohydrates across 3 small-to-moderate meals and 2–4 snacks throughout the day, with an evening snack usually necessary to prevent accelerated overnight ketosis. 1
Emphasize monounsaturated and polyunsaturated fats while limiting saturated fats and avoiding trans fats entirely. 1
Do not reduce carbohydrates below 175 g/day, as intakes below this threshold may compromise fetal growth when total energy intake is inadequate. 1
For overweight women, caloric needs are approximately 30–32 kcal/kg of pre-pregnancy body weight, plus an additional 340 kcal/day in the second trimester, totaling approximately 2,000–2,200 kcal/day. 1
Physical Activity
- Prescribe at least 150 minutes of moderate-intensity aerobic activity weekly, spread throughout the week. 1, 3
Blood Glucose Monitoring
Self-Monitoring Protocol
Check fasting glucose daily upon waking and postprandial glucose after each main meal (breakfast, lunch, dinner). 1
Choose either 1-hour postprandial OR 2-hour postprandial measurements consistently—do not alternate between the two. 1
Glycemic Targets
- Fasting glucose < 95 mg/dL 1, 2, 3
- 1-hour postprandial < 140 mg/dL 1, 2, 3
- 2-hour postprandial < 120 mg/dL 1, 2, 3
HbA1c Monitoring
HbA1c has limited utility in GDM management and should NOT replace blood glucose monitoring, because macrosomia results primarily from postprandial hyperglycemia, which HbA1c may not adequately detect. 1
If HbA1c is used, measure monthly with a target < 6% (42 mmol/mol) if achievable without significant hypoglycemia. 1
Pharmacologic Management
When to Initiate Pharmacotherapy
Add pharmacologic treatment if glycemic targets are not achieved within 1–2 weeks of optimized lifestyle modifications. 1, 2
Also initiate pharmacotherapy if ultrasound shows excessive fetal growth (fetal abdominal circumference ≥ 75th percentile for gestational age). 1
First-Line Agent: Insulin
Insulin is the preferred and recommended first-line pharmacologic agent because it does not cross the placenta to a measurable extent. 1, 2, 3
Calculate the initial total daily insulin dose as 0.7–1.0 units/kg of current maternal weight. 1
Allocate approximately 40% as basal insulin and 60% as prandial insulin. 1
Titrate insulin frequently (weekly to bi-weekly) to match the 5% weekly increase in insulin requirements that occurs from diagnosis through week 36 of gestation, often resulting in a doubling of the initial dose by late pregnancy. 1
Oral Agents: Not Recommended as First-Line
Metformin
Metformin is NOT recommended as first-line therapy because it crosses the placenta, producing umbilical-cord concentrations equal to or higher than maternal levels. 1
The MiG-TOFU follow-up study showed that children aged 9 years exposed in utero to metformin had higher body-mass index, waist-to-height ratio, and waist circumference compared with those exposed to insulin. 1
Approximately 25–28% of women fail to achieve glycemic targets when treated with metformin alone, necessitating additional therapy. 1
Discontinue metformin immediately and switch to insulin if the patient develops hypertension, preeclampsia, or any sign of placental insufficiency, to prevent fetal growth restriction or acidosis. 1
Glyburide
Glyburide is NOT recommended as first-line therapy because it crosses the placenta, with fetal cord concentrations reaching 50–70% of maternal levels. 1
Meta-analyses demonstrate that glyburide use is associated with higher rates of neonatal hypoglycemia, macrosomia, and increased fetal abdominal circumference compared with insulin or metformin. 1
Glyburide failed to meet non-inferiority criteria versus insulin for a composite neonatal outcome (hypoglycemia, macrosomia, hyperbilirubinemia). 1
About 23% of women on glyburide do not reach glycemic targets. 1
When Oral Agents May Be Considered
Oral agents can be used when insulin administration is impractical or unsafe because of cost, language barriers, limited health literacy, or cultural factors. 1
If a well-informed patient declines insulin after comprehensive counseling, an oral agent may be offered as an alternative. 1
When an oral agent is chosen, metformin is preferred over glyburide because it is linked to lower incidences of neonatal hypoglycemia and macrosomia. 1
Patients must be counseled that all oral agents cross the placenta and that long-term offspring safety data are lacking. 1
Fetal Surveillance
Ultrasound Monitoring
Begin ultrasound monitoring of fetal abdominal circumference in the second and early third trimesters and repeat every 2–4 weeks. 1, 2
When fetal abdominal circumference is < 75th percentile (normal growth), a less intensive management approach may be adopted, but self-monitoring of blood glucose should continue. 1
When fetal abdominal circumference is ≥ 75th percentile (excessive growth), lower glycemic targets or intensify pharmacologic therapy. 1
Fetal Movement Monitoring
Teach mothers to monitor fetal movements during the last 8–10 weeks of pregnancy and report immediately any reduction. 1
Women whose fasting glucose exceeds 105 mg/dL or who progress beyond term require heightened surveillance for fetal demise. 1
Maternal Surveillance
Measure blood pressure and urinary protein at each prenatal visit to detect preeclampsia, as the risk of hypertensive disorders is increased 1.6-fold in women with GDM. 1, 2
Fasting urine ketone testing may help detect inadequate caloric or carbohydrate intake in women on calorie-restricted diets. 1
Intrapartum Management
Monitor maternal blood glucose every 1–2 hours during labor, targeting a range of 80–110 mg/dL to reduce the risk of fetal hypoxia and neonatal hypoglycemia. 1
If capillary glucose exceeds 180 mg/dL (10 mmol/L) during labor, administer an insulin bolus. 1
If glucose exceeds 297 mg/dL (16.5 mmol/L), delay non-urgent procedures and give corrective insulin. 1
Delivery Timing
Delivery at 39–40 weeks of gestation is appropriate for women with diet-controlled GDM meeting glycemic targets. 1
Delivery at 39 weeks of gestation is recommended for women requiring insulin or with poor glycemic control, as postponing delivery beyond 40 weeks in this context increases perinatal mortality. 1
Postpartum Follow-Up
Immediate Postpartum (4–12 Weeks)
Test for persistent diabetes or prediabetes at 4–12 weeks postpartum using a 75-g oral glucose tolerance test (OGTT) with non-pregnancy diagnostic criteria. 1, 2, 3
Do NOT use HbA1c at this visit because the concentration may still be influenced by changes during pregnancy and/or peripartum blood loss. 1
Long-Term Surveillance
Women with a history of GDM have a 50–70% risk of developing type 2 diabetes over 15–25 years. 1, 2
Perform lifelong screening for diabetes at least every 3 years using standard non-pregnant criteria (annual HbA1c, annual fasting plasma glucose, or triennial 75-g OGTT). 1
Breastfeeding and Contraception
Strongly encourage breastfeeding because it provides immediate nutritional and immunologic benefits and may confer longer-term metabolic advantages for both mother and child. 1, 2
Review contraception options regularly for all women of childbearing age, including the postpartum period, to prevent unintended pregnancies and allow appropriate inter-pregnancy intervals. 2
Common Pitfalls to Avoid
Do not delay insulin initiation in women with poor glycemic control on lifestyle modifications—waiting beyond 1–2 weeks increases the risk of fetal macrosomia and other complications. 1, 2
Do not start oral agents before attempting insulin, as the safety concerns of placental transfer outweigh convenience. 1
If glycemic targets are not met within 1–2 weeks of oral therapy, transition promptly to insulin or add insulin to the regimen. 1
Recognize that glyburide carries the poorest safety profile among available agents, with the highest rates of neonatal hypoglycemia and macrosomia. 1
Do not rely solely on HbA1c for monitoring, as it represents an average and may not capture physiologically relevant postprandial glycemic excursions in pregnancy. 1, 2
Do not use metformin for polycystic ovary syndrome beyond the first trimester. 2
Team-Based Care
Refer patients to specialized centers or interprofessional teams when available, given the complexity of insulin management during pregnancy. 2
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. 1