In 2008 the HAPO (Hyperglycemia and Adverse Pregnancy Outcomes) data was published and validated the 75-g 2-h “one-step” screening. The 75-g 2-h test is more convenient, better tolerated, and more sensitive for identifying pregnancies at risk for adverse outcome than the 100-g 3-h oral GTT. Increased sensitivity is primarily related to the fact that only one elevated glucose value is needed for a positive test [8] although the cutoffs are also slightly lower. Since this publication in 2008, much controversy has existed about one-step versus two-step testing. Most organizations except the American Congress of Obstetrics and Gynecology (ACOG) recommend using one-step testing (International Association of Diabetes and Pregnancy Study Groups(IADPSG)), World Health Organization, The Endocrine Society, Australian Diabetes in Pregnancy Society and more). The American Diabetes Association (ADA) recommends one- or two-step testing. While the goal of this chapter is not to promote one method over the other, one-step testing has many advantages including earlier diagnosis and thus less delay in intervention as a second oral test is not needed. In addition further studies continue to show that one-step testing may identify more women at increased risk of adverse outcomes [9–11]. More research is needed to explore the cost-effectiveness of the testing.

In our case, the patient was diagnosed with GDM, and initially dietary changes helped but she ultimately needed more treatment than diet and exercise. Once the diagnosis of GDM is made, glucose monitoring with four times daily (fasting and 1- or 2-h postprandial) measurements can help assess the effectiveness of dietary interventions described below. One- or two-hour postprandial glucose can be used although our center uses 1-h as the 2-h assessment may miss a peak in glucose. Postprandial glucose values are considered the gold standard in pregnancy based on data that assessed outcomes for preprandial versus postprandial glucose in GDM patients. Postprandial measurements resulted in a lower HgA1c and less incidence of macrosomia and cesarean delivery for cephalopelvic disproportion as compared to preprandial values [12]. Goal values are variable as hyperglycemia is a continuum and there are no values below which to prevent all complications [8]. The ADA and ACOG recommend fasting blood glucose ≤95 mg/dL, 1-h postprandial ≤140 mg/dL, and 2-h postprandial ≤120 mg/dL.

The goal of dietary changes is to decrease hyperglycemia, prevent ketosis, provide adequate weight gain based on maternal BMI, and prevent fetal macrosomia [13]. Dietary changes include distribution of calories into three small to moderate meals and two to four snacks per day. Smaller frequent meals decrease postprandial hyperglycemia. Caloric intake is based on maternal BMI; see Table 2. Once the caloric needs are calculated, the distribution of calories is recommended by the American Diabetes Association (ADA) to be about 40 % carbohydrates evenly distributed among meals and snacks, 20 % protein, and 40 % fats with <7 % saturated fats comprising total calories. The least information is known about calorie intake for obese women (BMI > 30) but the ADA recommends restricting caloric intake by 30 % [14].

If there are no medical contraindications to exercise, moderate physical activity is recommended in patients with GDM. Data to support this recommendation is limited in pregnant patients, but in one study pregnant GDM patients showed a decrease in mean HgA1c; fasting and 1-h glucose were seen after 6 weeks of arm ergometry three times a week for 20 min [15].

Follow-up of patients during pregnancy with GDM should include measurement of maternal weight and fetal assessment (see Case #2), but both HgA1c and daily measurement of ketones are optional. HgA1c in pregnancy is lowered by the increase in red cell mass, increase in red blood cell turnover, ethnicity, as well as anemia [16]; therefore, it is not usually helpful in monitoring of patients with GDM. If noncompliance is suspected, then HgA1c may be helpful to correlate with daily logs. Ketones have a controversial association with poor cognitive development on the fetus [17, 18], yet other studies in nondiabetics have shown no difference in long-term neonatal outcome. Development of ketones in GDM is usually from starvation ketosis and not diabetic ketosis as can be the case in preexisting type 1 diabetes. Ketones may be useful to follow especially if a patient is losing weight as strict adherence in order to avoid medications such as insulin result in ketones and weight loss. Maternal starvation and weight loss especially in GDM may lead to fetal growth restriction [19].

In this case, as insulin resistance increased with advancing gestation, the patient could not meet the goal glucose values and needed additional therapy. Oral hypoglycemic medication will be discussed in the following two cases but here insulin was recommended. Most commonly insulin is recommended when the glucose targets are not achieved. New evidence is developing that targeting patients when the fetal ultrasound measured abdominal circumference is more than 75 % may allow for prevention of fetal macrosomia as well. Meta-analysis of the two largest studies showed this approach limited the incidence of fetal macrosomia but increased the frequency of ultrasound and the number of patients requiring insulin therapy. The number of women with GDM needed to treat with insulin to avoid a newborn with abnormal birth weight was ten [20].

Insulin analogs best studied in pregnancy with good safety profiles and similar to human insulin are lispro (rapid acting), aspart (rapid acting), NPH (intermediate), and Levemir (long acting). Dosing of insulin depends on the patient weight, ethnicity, and timing of hyperglycemia. Generally 0.7–2 units/kg is used and this increases in later gestation as well. If a patients’ fasting glucose is elevated, NPH is usually recommended at bedtime, and if postprandial glucose is elevated, rapid-acting insulin is given with a meal. If both fasting and postprandial glucose are elevated, then both NPH and rapid-acting insulin are recommended. The distribution of insulin is about 50 % NPH and 50 % rapid-acting split between three meals. Rough estimates can be used to calculate doses by trimester: 0.7 units/kg up to 12 weeks, 0.8 units/kg up to 26 weeks, and 0.9–1.0 units/kg up to term. In an obese patient, these doses may need to be significantly increased. Twins (discussed in Case #2) will also need increased insulin dosing. Adjustments upward are generally 10–20 % if hyperglycemia persists. Many patients fear that insulin is a permanent treatment and fear injections into the subcutaneous fat especially near the fetus. Reassurance that insulin does not cross the placenta in significant amounts and needles are too small to reach the fetus should be reviewed. High serum glucose rapidly crosses the placenta and increases the risk of macrosomia.

Finally, this patient is diagnosed with impaired glucose tolerance after delivery and has a significantly increased lifetime risk of diabetes. About 20 % of women who have GDM in pregnancy will be diagnosed with IGT after delivery [21]. About 60 % of patients will develop type 2 diabetes after the index pregnancy with GDM. Modifiers that can help decrease that risk may include breastfeeding, weight loss, and exercise. Further studies are in progress to assess the specific decreased risk of T2 DM from breastfeeding [22].

Complications of gestational diabetes are preeclampsia, macrosomia, birth injury to the neonate from shoulder dystocia, maternal trauma from delivery including operative delivery, neonatal demise, and hypoglycemia. Management and care of diabetes decreases these risks. Careful monitoring of the pregnant gravida will be discussed in Case #2.