Gestational Diabetes Mellitus
Poorly controlled gestational diabetes is associated with an increase in the incidence of preeclampsia, polyhydramnios, fetal macrosomia, birth trauma, operative delivery, and neonatal hypoglycemia. There is an increased incidence of hyperbilirubinemia, hypocalcemia, and erythremia. Later development of diabetes mellitus in the mother is also more frequent.
Risk Factors for Gestational Diabetes
A family history of diabetes, especially in first degree relatives
Prepregnancy weight of 110 percent of ideal body weight (pregravid weight more than 90 kg) or more or weight gain in early adulthood.
Age greater than 25 years
A previous large baby (greater than 9 pounds [4.1 kg])
History of abnormal glucose tolerance
A previous unexplained perinatal loss or birth of a malformed child
The mother was large at birth (greater than 9 pounds [4.1 kg])
Polycystic ovary syndrome
Screening and diagnostic criteria
Screening for gestational diabetes should be performed at 24 to 28 weeks of gestation. However, it can be done as early as the first prenatal visit if there is a high degree of suspicion that the pregnant woman has undiagnosed type 2 diabetes (eg, obesity, previous gestational diabetes or fetal macrosomia, age >25 years, family history of diabetes).
50-g oral glucose challenge is given for screening and glucose is measured one hour later; a value >140 mg/dL (7.8 mmol/L) is considered abnormal. Women with an abnormal value are then given a 100-g, three-hour oral glucose tolerance test (GTT).
Criteria for Gestational Diabetes with Three Hour Oral Glucose Tolerance Test
*Any two or more abnormal results are diagnostic of gestational diabetes.
Treatment of gestational diabetes mellitus
Moderate caloric restriction may be useful in treating obese women (body mass index greater than 30 km/m2) with gestational diabetes. However, ketosis should be avoided.
The recommended caloric intake is 30 kcal per present weight in kg per day in pregnant women who are 80 to 120 percent of ideal body weight at the start of pregnancy. 24 kcal per present weight in kg per day in overweight pregnant women (120 to 150 percent of ideal body weight). 12 to 15 kcal per present weight in kg per day for morbidly obese pregnant women (>150 percent of ideal body weight). 40 kcal per present weight in kg per day in pregnant women who are less than 80 percent of ideal body weight.
Recommendations for calorie and carbohydrate distribution are 40 percent carbohydrate, 20 percent protein, and 40 percent fat.
Distribution of calories should be three meals and three snacks. In overweight women,
however, the snacks are eliminated.
The remaining calories should be distributed as 30 percent at both lunch and dinner, with
the leftover calories distributed as snacks. With this calorie distribution, 75 to 80 percent
of women with gestational diabetes can achieve normoglycemia.
Women should be encouraged to choose lean, low-fat foods and to avoid excessive weight gain. Obesity can cause excessive fetal growth and worsens glucose intolerance.
Glucose monitoring and goal concentrations
Women with gestational diabetes should measure blood glucose at home and keep a diet
diary. Blood glucose should be measured upon awakening and one hour after each meal. Two criteria should be met to assure that the degree of glycemic control is adequate to prevent macrosomia:
The fasting blood glucose concentration should be less than 90 mg/dL. The one-hour
postprandial blood glucose concentration should be less than 120 mg/dL.
(HbA1c) should be measured every two to four weeks.
Control of blood glucose
Fifteen percent of women with gestational diabetes require insulin therapy because of
elevated blood glucose concentrations despite dietary therapy. Insulin should be initiated
when the fasting blood glucose is greater than 90 mg/dL and the one-hour postprandial blood glucose is greater than 120 mg/dL on two or more occasions within a two-week interval despite dietary therapy.
Preprandial blood glucose concentrations below 90 mg/dL and one-hour postprandial
concentrations below 120 mg/dL minimize the incidence of macrosomia.
If insulin is required because the fasting blood glucose concentration is high, an
intermediate-acting insulin, such as NPH insulin, is given before bedtime. If both preprandial and postprandial blood glucose concentrations are high, then a four-injection per day regimen should be initiated.
Adjustments in the insulin doses are based upon the results of self blood glucose monitoring. Insulin resistance increases as gestation proceeds, requiring an increase in insulin dose.
Counting fetal movements is a simple way to assess fetal well-being. Fewer than ten fetal movements in a 12-hour period is associated with a poor outcome. Fetal surveillance should be initiated in women in whom gestational diabetes is not well-controlled, who require insulin, or have other complications of pregnancy (eg, hypertension, adverse obstetric history).
Women with good glycemic control and no other complications ideally will deliver at 39 to 40 weeks of gestation.
Macrosomia and cesarean delivery.
The risk of macrosomia among women with untreated GDM is 17 to 29 percent. Cesarean delivery for the prevention of shoulder dystocia is recommended when the estimated fetal weight is greater than 4.5 kg.
The great majority of women with gestational diabetes proceed to term and have a spontaneous vaginal delivery. The maternal blood glucose concentration should be maintained between 70 and 90 mg/dL. Insulin can usually be withheld during delivery, and an infusion of normal saline is usually sufficient to maintain normoglycemia.
Nearly all women with gestational diabetes are normoglycemic after delivery. However, they are at risk for recurrent gestational diabetes, impaired glucose tolerance, and overt diabetes. One-third to two-thirds of women will have gestational diabetes in a subsequent pregnancy. Women with gestational diabetes have an incidence of type 2 diabetes in the first five years postpartum of 47 to 50 percent.
After delivery, blood glucose should be measured to ensure that the mother no longer has
hyperglycemia. Fasting blood glucose concentrations should be below 115 mg/dL and one hour postprandial concentrations should be below 140 mg/dL. A woman with gestational diabetes should be able to resume a regular diet. However, she should continue to measure blood glucose at home for a few weeks after discharge.
Six to eight weeks after delivery, or shortly after cessation of breast feeding, all women with previous gestational diabetes should undergo an oral glucose tolerance test. A two-hour 75 gram oral glucose tolerance test is recommended.