Gestational Diabetes

Gestational Diabetes

A subset of pregnant women (2–8% depending on ethnic group, body habitus, and family history for diabetes) develop impaired glucose tolerance with advancing gestation. Gestational diabetes (GDM) results from sluggish first-phase insulin release in lean pregnant women, in addition to excessive resistance to the action of insulin on glucose utilization, which may predate pregnancy. In overweight women with glucose intolerance, insulin sensitivity decreases with advancing gestation more than in overweight pregnant controls, but circulating insulin levels may be increased, although insulin secretion is actually inadequate in relation to the hyperglycemia. Diagnostic strategies for GDM are outlined in table 1. Once the diagnosis has been made, the patient should be placed on a diabetic diet modified for pregnancy: 25–35 kcal/kg ideal weight, 40–55% carbohydrate, 20% protein, and 25–40% fat, and most patients should be taught to count their carbohydrates. Calories are distributed over 3 meals and 3–4 snacks (table 2) and patients are asked to record their daily food intake. The goal of therapy is not weight reduction but prevention of both fasting and postprandial hyperglycemia. If 1- or 2-hour postprandial self-monitored blood glucose (SMBG) values are consistently greater (respec- tively) than 7.2 or 5.8 mmol/l (130 or 105 mg/dl), therapy is begun with human insulin (new oral agents with limited placental transfer are under study), and the patient is managed as if insulin-dependent.

A large proportion of women with GDM will progress to type 2 diabetes (DM) in the 2–20 years after pregnancy. Risk factors for progression include degree of glucose intolerance during and soon after pregnancy, elevated fasting glucose levels, need for insulin therapy during pregnancy, obesity, and choice of contraception. Follow-up studies indicate that 5–15% of nonobese women with GDM will need treatment in 5–20 years, compared to 35–50% of gesta- tional diabetic women with a body weight greater than 120% of ideal. Studies

Table 1. Screening and diagnosis of gestational diabetes Risk for GDM should be ascertained at the first prenatal visit

Low risk: Universal vs. selective screening remains controversial; most diabetes organizations state that blood glucose testing is not normally required if all of the following characteristics are present:

Member of an ethnic group with a low prevalence of GDM No known diabetes in first-degree relatives Age =25 years Weight normal before pregnancy No history of abnormal glucose metabolism or poor pregnancy outcome

Average risk: Perform BG testing at 24–28 weeks using one of the following: One-step protocol – 75 g, 2 h OGTT on all women: F =5.3 mmol/l (95 mg/dl)

2 h =8.6 (155) Two-step protocol – 50 g, 1 h plasma glucose on all women; if test done in fed state, threshold ? 7.2 mmol/l (130 mg/dl); if test done in fasting state, threshold ?7.8 mmol/l (140 mg/dl); then 100 g, 3 h OGTT done in fasting state:

1 h =10 (180)

2 h =8.6 (155) 3 h =7.8 (140) If one value abnormal, repeat test in 4 weeks

F =5.3 mmol/l (95 mg/dl)

1 h =10 (180)

High risk: Perform testing as soon as feasible; if negative, repeat at 24–28 weeks Adapted from Summary and Recommendations, 4th International Workshop-Conference

on GDM: Diabetes Care 1998:21(suppl 2):B162.

are underway to determine if type 2 DM can be delayed or prevented in these women by regular exercise, dietary control, or insulin enhancers. Patients with GDM should undergo a 75-gram 2-hour glucose tolerance test at 6–10 weeks after delivery to guide future medical management. Diagnostic criteria for nonpregnant individuals are presented in table 3.