University of Toronto - Faculty of Medicine

 

Author
The revision of this chapter was prepared by Denice S. Feig, MD, MSc, FRCPC

 

• Hyperglycemia with onset or first recognition during pregnancy
• Occurs in 2-4% of all pregnancies, but can be up to 18% in populations with very high incidence of Type 2 DM, such as Aboriginal populations

 

• Increases in estrogen, progesterone, prolactin, cortisol, human placental lactogen, free fatty acids and triglycerides cause insulin resistance.
• Normally, there is increased pancreatic insulin secretion to overcome insulin resistance.
• Women with GDM have both increased insulin resistance and impaired insulin release which leads to hyperglycemia.

 

• Obesity (BMI ≥ 30 kg/m2)
• A first degree relative with type 2 diabetes
• Member of a high risk population (i.e. Aboriginal, Hispanic, South Asian, Asian, African)
• Older maternal age (≥ 35 years)
• A previous infant with macrosomia (birth weight 4 kg or greater)
• Previous history of gestational diabetes
• Polycystic ovary syndrome
• Acanthosis nigricans
• Corticosteroid use

 

• Increased risk of macrosomia which may result in shoulder dystocia, brachial plexus injury, and clavicular fracture
• Increased frequency of maternal hypertensive disorders
• Increased rate of Cesarean section to avoid birth trauma
• Neonatal hypoglycemia, hyperbilirubinemia, hypocalcemia, polycythemia, respiratory distress syndrome
• Children at increased risk of obesity, impaired glucose tolerance and diabetes in late adolescence and young adulthood

 

• Screening for GDM is controversial. The literature suggests that about 50% of cases will be missed if only women with recognized risk factors are screened. Selective screening can be impractical and results in some missed diagnoses.
• The Canadian Diabetes Association (CDA) recommends screening all women at 24-28 weeks. They suggest screening women with multiple risk factors in the first trimester and if negative, rescreening in subsequent trimesters.
• The Society of Obstetrics and Gynecology of Canada (SOGC) state there is not enough evidence to recommend a single approach and recommend either screening all but low risk women or not screening is acceptable.
• The American Diabetes Association recommends screening all women except those <25 years with no risk factors.
• The Canadian Task Force for Preventive Health Care felt the evidence for universal screening was not adequate and recommend that the decision to screen be made on an individual basis.
• Screening Test: 50g oral glucose load given any time of day. If plasma glucose is ≥ 7.8 mmol/L, then an oral glucose tolerance test (75gm or 100gm OGTT) should be done for diagnosis. If the plasma glucose is ≥ 10.3 mmol/L, the diagnosis of GDM is made and there is no need to do the OGTT.

 

Canadian Diabetes Association Guidelines:
Using the normative data in pregnant women from two studies, one multicentered study of Caucasian women in Europe, and another of Latino women in California, the CDA recommends

• 2 hr 75g oral glucose tolerance test
• Diagnosis is made if two or more values of the following are met or exceeded:

  Fasting	≥ 5.3 mmol/L
  1 hr	≥ 10.6
  2 hr	≥ 8.9

• If one value is met or exceeded, the diagnosis is impaired glucose tolerance of pregnancy.

Society of Obstetrics and Gynecologists of Canada Guidelines:

• May do a 3 hr 100g OGTT using either the NDDG criteria or the Carpenter and Coustan criteria or 2 hour 75g OGTT using the American Diabetes Association criteria.
• Diagnosis is made if two or more values of the following are exceeded:

  	NDDG criteria	Carpenter & Coustan criteria	ADA criteria
  Fasting	≥ 5.8 mmol/L	5.3	5.3
  1 hr	≥ 10.6	10.0	10.0
  2 hr	≥ 9.2	8.6	8.6
  3 hr	≥ 8.1	7.8

• If one value is met or exceeded, the diagnosis is impaired glucose tolerance of pregnancy.
• Worldwide, the 2 hr 75g OGTT is used most commonly for both the screening and diagnostic test. Data from the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study correlating glucose levels with outcomes showed that increases in glucose on the OGTT are associated with an increased risk of fetal hyperinsulinemia, birth weight, cesarian deliveries and neonatal hypoglycemia. These increases in risk were continuous. It is hoped that international consensus regarding new diagnostic criteria based on the HAPO data, will be made soon.

 

• Dietary counseling by a registered dietician aimed at normalizing maternal glucose levels and ensuring normal weight gain in mother (see Institute of Medicine guidelines http://www.iom.edu/CMS/3788/48191/68004.aspx) and fetus.
• Fasting and postprandial self monitoring of blood glucose is advised.
• Goals: FBS< 5.3 mmol/L, 1 hr PC meals < 7.8 mmol/L, 2 hr PC meals < 6.7 mmol/L
• If glycemic goals cannot be achieved on diet alone, human insulin should be instituted.
• Insulin lispro (Humulog) does not cross the placenta at moderate doses, and can be used safely in pregnancy.
• Placental transfer of insulin aspart (NovoRapid) has not been assessed but aspart has been shown to lower postprandial glucose levels in women with GDM.
• The safety of insulin glargine (Lantus) has not been tested in pregnancy and should be avoided.
• Glyburide does not appear to cross the placenta and has been used after the first trimester with good glycemic control and fetal outcomes. However further studies are needed before recommending its use to everyone. It may be considered in patients who refuse insulin.
• Metformin has been used in a randomized trial with no increase in perinatal complications when compared with insulin. Metformin does cross the placenta, and results on the infants at 2 years follow-up will provide more long term data. Metformin may be considered in patients who refuse insulin, after appropriate discussion.

Breastfeeding

• Glyburide is not found in breast milk. Metformin crosses into breast milk but at very low concentration. They are both compatible with breastfeeding.
• Breastfeeding has been shown to reduce offspring obesity and prevent the development of type 2 diabetes.

 

• Some women with GDM actually have unrecognized type 2 diabetes. To diagnose these patients a 2 hr 75g OGTT or fasting plasma glucose is recommended within 6 months of delivery.
• Women with GDM are at increased risk of developing diabetes later in life. The cumulative incidence of type 2 diabetes is between 2.6% and 70%, depending on the time since the index pregnancy and the population studied. The incidence increases markedly in the first five years after delivery, and appears to plateau after ten years. Rates of progression appear to be highest among women with elevated fasting glucose levels in pregnancy, and in Latin and Native American women with gestational diabetes.

Management

• Encourage maintenance of normal weight, exercise and avoidance of drugs causing insulin resistance (i.e. steroids and nicotinic acid).
• Counsel on symptoms of diabetes.
• Screen for diabetes with FBS at least every three years, or more frequently in those with impaired glucose tolerance or impaired fasting glucose.
• Screen for components of metabolic syndrome as women with GDM are at increased risk.
• Reassess glucose tolerance prior to subsequent pregnancies.

Offspring

• There is increasing evidence that offspring are at increased risk of obesity and impaired glucose tolerance. Breastfeeding may lower this risk. Children should be encouraged to eat healthy and exercise.

References

1. Canadian Diabetes Association Clinical Practice Guidelines Expert Committee. Canadian Diabetes Association 2008 Clinical Practice Guidelines for the Prevention and Management of Diabetes in Canada. Can J Diabetes 2008;32(suppl 1):S168-S180.
2. Gestational Diabetes Mellitus. Diabetes Care 2004;27(Supp 1):S88-S90.
3. Berger H, Crane J, Farine D et al. Screening for gestational diabetes mellitus. J Obstet Gynaecol Can. 2002;24:894-912.