Medical management of GDM
Most cases of GDM can be managed by lifestyle measures alone, including careful attention to dietary principles and regular exercise during pregnancy. Blood glucose is monitored before and one or two hours after meals backed by regular measurement of HbA1c. Insulin is the recommended first line of treatment if glycemic targets are exceeded, although there is increasing evidence that oral agents (metformin or glyburide) are safe in this situation. The requirement for insulin usually ends with delivery, but diabetes is likely to recur with subsequent pregnancies or later in life, and appropriate advice and long-term monitoring are needed.
Most cases (70-85%) of mild gestational diabetes (GDM) can be managed by lifestyle changes (specifically, medical nutrition therapy - MNT - and exercise). Pharmacologic agents are recommended if lifestyle interventions alone fail to control glucose levels. The recommended glycemic targets for patients with GDM are as follows: Fasting blood glucose ≤ 5.3 mmol/L (95 mg/dl); 1h post-prandial ≤ 7.8 mmo/L (140 mg/dl) or 2h post-prandial ≤ 6.7 mmol/L (120 mg/dl) .
Medical Nutrition Therapy and Exercise:
MNT is sufficient to manage mild GDM in most instances. It should be offered in consultation with an experienced nutritionist and in a culturally sensitive manner. The general principles are as follows:
- Avoid processed, high glycemic index foods; sugars, juices, and most fruits
- Favor low carbohydrate, high fiber foods (vegetables should be the primary source of carbohydrates)
- Small, frequent meals (to help avoid/minimize glucose excursions)
- Count carbohydrates and adjust based on pre and peak post-meal glucose levels
There are no published data on the minimum quantity of daily carbohydrates that is safe in pregnancy. The Institute of Medicine (IOM) recommends 175 g/day, but this recommendation was issued for non-diabetic women. Low carbohydrate diets (i.e <35% of daily calorie intake) were found to be safe in GDM , while associated with a lesser need for insulin and lower incidence of fetal macrosomia .
There are also no published goals for pregnancy weight gain in GDM or women with diabetes generally, but given the fact that GDM is diagnosed late in pregnancy, and many women with GDM are overweight or obese pre-pregnancy, it is generally recommended to use the IOM guidelines for pregnancy weight gain, based on pre-pregnancy Body Mass Index. Specifically:
- Normal pre-pregnancy weight: Suggested weight gain 25-35 pounds
- Underweight women : Suggested weight gain 28-40 pounds
- Overweight women : Suggested weight gain 15-25 pounds
- Obese women: Suggested weight gain 11-20 pounds
Finally, exercise can be a useful adjunct to diet and may help improve insulin sensitivity and blood glucose levels in GDM. The American College of Obstetricians and Gynecologists recommends an average of 30 minutes per day in non-diabetic women. In the absence of contra-indications, a similar prescription should be made for patients with GDM .
Monitoring of blood glucose during pregnancy: Women should be encouraged to check finger stick blood glucoses before and one or two hours after meals. Bedtime checks and 2-3 AM checks (if indicated) can be tailored to the individual patient. Frequent monitoring of the glycated hemoglobin (HbA1c) level may also help guide therapy and motivate/get the patient to target more rapidly , although it is not used routinely for management.
Pharmacologic management: If MNT and lifestyle changes are not sufficient to maintain the blood glucose at the recommended targets within 1-2 weeks, the ADA and AACE generally recommend the initiation of insulin .
Oral hypoglycemic agents are still not widely adopted and are not FDA approved for the management of GDM. Despite those reservations, glyburide (glibenclamide) and metformin are increasingly used by the Ob/Gyn community. Their pros include ease of use, low cost, and less anxiety/teaching requirements for patients.
Use of oral agents in pregnancy
Oral agents do not control post-prandial blood glucose excursions as effectively as insulin, and some concerns remain about fetal safety (specifically neonatal hypoglycemia secondary to fetal hyperinsulinemia with sulfonylureas), but the data remain inconsistent among studies .
Metformin was shown by a recent trial to be a viable option to insulin, and while there has not been a systematic evaluation of its safety in pregnancy, its track record shows no indication of teratogenicity. It is recommended by both NICE (National Institute for Health and Clinical Excellence) and CDA (Canadian Diabetes Association) as a potential alternative to insulin when lifestyle interventions alone fail .
In addition, these associations suggest glyburide (glibenclamide) as another option, with the caveat that dose titration may jeopardize the need for rapid control of blood glucose in GDM to avoid fetal macrosomia.
Insulin Options in Pregnancy:
For basal insulin requirements, both insulin NPH and detemir can be used in pregnancy. The safety of glargine has not been established in this setting, although it is commonly used. For prandial and correction insulin requirements, regular human insulin, as well as the analogs lispro and aspart can be used. Guidelines for starting doses –based on pregnancy stage- are summarized in Table 1. Typically, 50% of the total daily dose is used for basal requirements and 50% for prandial requirements (divided into three doses), with frequent adjustment to dosing until glycemic targets are reached.
Table 1: Insulin dosing guidelines during pregnancy. These should be tailored to the individual patient. Adapted from Ref. 
|Weeks Gestation||Total Daily Dose Insulin|
|1-13 weeks||0.7 x Wt (Kg)|
|14-26 weeks||0.8 x Wt (Kg)|
|27-37 weeks||0.9 x Wt (Kg)|
|38 weeks-delivery||1.0 x Wt (Kg)|
Post-partum and Lactation| There is typically no need for insulin for most women with GDM, a but they remain at increased risk of developing diabetes in subsequent pregnancies or later in life, and appropriate counselling and advice should be provided.
^ American Association of Clinical Endocrinologists Medical Guidelines for Clinical Practice for developing a diabetes mellitus comprehensive care plan. Endocr Pract. 2011 Mar-Apr;17 Suppl 2:1-53.
^ American Diabetes Association. Standards of Medical Care in Diabetes. Diabetes Care. 2013;36(suppl 1):S11-66.
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^ Jovanovic L, Savas H, Mehta M, Trujillo A, Pettitt DJ. Frequent monitoring of A1C during pregnancy as a treatment tool to guide therapy. Diabetes Care. 2011 Jan;34(1):53-4.
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