A 34-year-old Asian female presented for a visit at 26 weeks to her obstetrician for follow-up care. This was her second pregnancy. The patient’s pregnancy had been uncomplicated except for some mild morning sickness in the first trimester which resolved. Her last pregnancy went smoothly and she delivered an 8 lb 6 oz baby at 40 weeks gestation. She expressed concern about her weight gain and mentioned that her mother has type-2 diabetes. Her weight at this visit is 162 lbs (pre-pregnancy 135 lbs ) her height was 5 ft 2 in. Her blood pressure was 105/68 and she had no edema and a gravid abdomen. The patient underwent a 2 h 75 g oral glucose tolerance test which came back with the following values:

Based on these results the patient was diagnosed with gestational diabetes mellitus. The patient was referred to a diabetes educator (RD, CDE) and given a meal plan containing 40 % carbohydrate, 20 % protein, and 40 % fat (1,900 calories) with three meals and two snacks. She was also taught home glucose monitoring and was instructed to test fasting and 1 h postprandially. Her Hba1c came back at 5.5 %.

The patient returned 1 week later for follow-up at 27 weeks and has showed good dietary compliance (with detailed food records) and appropriate testing intervals. Fasting values were 97–100 mg/dl and 1 h readings 145–158 mg/dl postmeals. Urine ketones were negative and the patient had lost 2 lbs.

The patient was started on NPH insulin 7 units at night (weight based approx 0.8 units kg). She followed up 1 week later and her fasting glucose was down to 88 mg/dl on most mornings. Postmeal readings were now in the 125–130 range. Continued weekly follow-up revealed increasing postprandial fingersticks and lispro was added at breakfast, lunch, and dinner at 30 weeks. Total pregnancy weight gain was 30 lbs and the patient delivered a healthy baby at 39 weeks weighing 8 lbs. No hypoglycemia was noted for mom or baby during labor and delivery or postpartum. Mom was planning to breast feed.

At postpartum follow-up at 6½ weeks, mom and baby were doing well with breastfeeding. Follow-up 2 h 75 g oral glucose tolerance test was performed and revealed:

Normal pregnancy is characterized by mild fasting hypoglycemia, postprandial hyperglycemia, and elevated serum insulin levels. This increased basal level of plasma insulin (insulin resistance) is associated with several unique responses to glucose ingestion. For example, after an oral glucose meal, gravid women demonstrate prolonged hyperglycemia and hyperinsulinemia as well as lower glucagon levels [1].

The factors responsible for insulin resistance are not completely understood. Progesterone and estrogen may act, directly or indirectly, to mediate this resistance. Plasma levels of placental lactogen increase with gestation, and this protein hormone is characterized by growth hormone-like action that may result in increased lipolysis with liberation of free fatty acids [2]. Other diabetogenic hormones including growth hormone, corticotropin-releasing hormone, placental lactogen, and progesterone, as well as increased maternal adipose deposition, decreased exercise, and increased caloric intake likely contribute to the resistance. The increased concentration of circulating free fatty acids also may aid increased tissue resistance to insulin [3].

Insulin resistance reaches maximal levels in the third trimester and thus guidelines for screening are typically at this point in pregnancy (24–28 weeks gestation). Women with higher degrees of risk for GDM include the following: strong family history of type-2 DM, prior personal history of GDM, history of a large baby at delivery, member of a higher risk ethnic group, obesity, and polycystic ovarian syndrome [4].

The prevalence of gestational diabetes is typically quoted as 3–5 % but in some studies higher percentages are reported. The prevalence varies worldwide and among racial and ethnic groups, generally in step with the prevalence of type-2 diabetes. In the USA, prevalence rates are higher in African American, Hispanic American, Native American, and Asian women than in white women [5]. Prevalence also varies because of differences in screening practices (universal versus selective screening), population characteristics (e.g., average age and body mass index (BMI) of pregnant women), testing method, and diagnostic criteria. Prevalence has been increasing over time, possibly related to increases in mean maternal age and weight.

Identifying pregnant women with diabetes is important because diagnosis with appropriate therapy can decrease fetal and maternal morbidity, particularly macrosomia. A study was performed which included 1,000 women with mild gestational diabetes in which subjects were randomly assigned to a group in which patients and providers were informed of the diagnosis and treatment was initiated or to a group in which patients and providers were blinded to the diagnosis and thus routine care was provided. Infants of women in the treatment group had significantly lower rates of perinatal complications (e.g., death, shoulder dystocia, bone fracture, nerve palsy; 1 % vs. 4 %) and a lower rate of macrosomia (10 % vs. 21 %) [5].

The purpose of screening is to identify asymptomatic individuals with a high probability of having or developing a specific disease. Screening for GDM is usually performed in the United States as a two-step process Step one identifies individuals at increased risk for the disease so that step two, diagnostic testing, which is definitive but usually more complicated or costly than the screening test, can be limited to individuals with a positive initial screen. Alternatively, a diagnostic test can be administered to all individuals, which is a one-step process. Currently different organizations have different approaches to screening as listed below and procedure choice is continuing to be debated: