Obstetrics in Family Medicine: A Practical Guide (Current Clinical Practice) 2nd ed.

15. Diabetes in Pregnancy

Paul Lyons¹

(1)

Department of Family Medicine, University of California, Riverside, Riverside, CA, USA

Key Points

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Background

DM (hyperglycemia secondary to either insulin deficiency or relative insulin insensitivity) is a significant medical condition with a potentially profound impact on pregnancy. Uncontrolled diabetes prior to or early in the course of pregnancy is associated with a variety of birth defects, including renal, gastrointestinal, cardiac, central nervous system, and skeletal abnormalities (see Table 15.1). The presence of diabetes may alter the interpretation of some prenatal tests including α-fetoprotein and obstetric triple screen. Pregnancy may, in turn, affect the course of diabetes, worsening glucose control in patients with pre-existing diabetes.

Table 15.1

Congenital abnormalities associated with diabetes

DM may be classified as type 1 diabetes, associated with pancreatic failure and insulin deficiency; type 2 diabetes, associated with ineffective insulin utilization (generally associated with hyperinsulinemia); or gestational diabetes mellitus (GDM), which is diabetes first diagnosed or recognized in pregnancy (generally associated with insulin resistance and similar to type 2 diabetes). GDM is associated with increased glucose intolerance during the course of pregnancy. In most cases this glucose intolerance will resolve following pregnancy. Hormonal changes associated with pregnancy increase maternal glucose intolerance. Human placental lactogen decreases cellular glucose uptake and increases lipolysis. Estrogen and progesterone are also known to affect glucose metabolism although to a lesser extent than human placental lactogen.

Diagnosis

Diagnosis of types 1 and 2 DM is made prior to pregnancy. The diagnosis is made on the basis of documented hyperglycemia with either insulin deficiency (type 1) or insulin resistance (type 2). The diagnosis of GDM is generally made on the basis of oral glucose testing during the course of prenatal care, although, in some cases, the diagnosis may be made on the basis of fasting blood glucose values.

Screening for GDM is an area of some controversy. Most authorities recommend universal screening of all patients at 24–28 weeks’ gestation. Earlier testing for those patients identified as high risk (see Table 15.2) is suggested by some authorities but has limited data demonstrating improved outcomes.

Table 15.2

Risk factors for gestational diabetes

Initial screening is via 50 g glucose tolerance testing. Patients are not required to fast and do not need to alter their dietary intake. A standardized 50 g glucose load is administered orally and serum glucose level is tested at 1 h. The threshold for a positive screening test is also an area of some controversy and providers should be aware of the standard of care in their institution. Serum glucose values should be less than 130 or 140 mg/dL. The lower value has a higher sensitivity (will miss fewer true cases of diabetes) but is associated with a higher false-positive rate. The higher value reduces false-positive findings (has a higher specificity) but may have a lower sensitivity.

Regardless of which threshold is used, all patients with a positive screening test should undergo diagnostic testing with a 3-h 100 g oral glucose challenge test. Patients should eat a carbohydrate-rich or unrestricted diet for 3 days prior to testing but should fast the night before the test. A standardized 100 g oral glucose load is administered, and serum glucose levels are drawn fasting 1, 2, and 3 h following administration. There is debate concerning the threshold values for this test as well. The National Diabetes Data Group’s recommendation is presented in Table 15.3. According to this protocol, blood glucose levels should be below 105 mg/dL fasting and below 190 mg/dL, 165 mg/dL, and 145 mg/dL at 1 h, 2 h, and 3 h, respectively. The test is considered diagnostic if any two values exceed the threshold.

Table 15.3

Gestational diabetes diagnosis (100 g, 3-h oral glucose tolerance test)

Note: the diagnosis of gestational diabetes is made if any two values exceed the values listed in the table

Pregestational Diabetes

Management

Preconception Management

The management of pregestational diabetes ideally should begin during the preconception period. Preconception management should include discussion of the effects of diabetes on pregnancy as well as discussion of the effects of pregnancy on diabetes. Patients should be counseled concerning the risks of maternal hyperglycemia on the developing infant and the importance of strict glycemic control prior to and throughout the course of pregnancy.

Preconception management should also include classification of the severity of diabetes. The modified White’s classification system is shown in Table 15.4. This classification is based on four factors: (a) treatment regimen, (b) duration of disease or age of onset, (c) associated disease, and (d) diabetic complications.

Table 15.4

White’s classification of diabetes in pregnancy

Because of the association of poor glycemic control with an increased risk for congenital defects, all patients should be intensively monitored and tightly controlled prior to conception. Because of the complexity of achieving tight glycemic control, such efforts should begin well before anticipated conception when possible.

Oral hypoglycemic agents are not generally utilized during pregnancy. Patients managed on oral hypoglycemic agents prior to conception may require additional time (and education) to transition to the use of insulin. Patients may also require comprehensive diabetes education on diet, exercise, and blood glucose self-monitoring. Prenatal vitamins with folate should be prescribed as a part of preconception management as well.

Management in Pregnancy

For patients who did not receive preconception evaluation and treatment, all of the management just discussed should begin with the first prenatal visit. Because the early weeks of pregnancy are the period of organogenesis, rapid assessment and intervention are critical to improve outcomes. Patients may require more frequent visits and will probably benefit from intensive educational interventions, beginning with a review of the patient’s own knowledge of her disease and its management.

Diet

All patients with diabetes should be counseled concerning the role of diet in the management of diabetes. Although specific recommendations may vary between patients, general recommendations include the following:

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Insulin

Pharmacological management of diabetes in pregnancy generally utilizes a combination of intermediate- and short-acting insulin. This combination allows for more controlled adjustment of glycemic control than either oral hypoglycemic agents or long-acting insulin alone. The exact dose of insulin will be based on measured blood glucose values with target levels of less than 105 mg/dL fasting (95 mg/dL according to some authorities) and less than 120 mg/dL 2 h postprandial. Insulin should be adjusted as necessary to achieve these target levels. Tight glycemic control has been demonstrated to improve obstetrical outcomes but have also been associated with increased risk of hypoglycemia. For this reason, patients should be educated concerning the symptoms of hypoglycemia and the appropriate steps to be taken should hypoglycemia occur.

Oral Hypoglycemics

Although insulin has been the traditional pharmacologic treatment choice (and remains the most common choice) there is increasing acceptance of oral hypoglycemic medications in pregnancy. Glyburide, which does not cross the placenta, is the most common oral hypoglycemic agent used in pregnancy. Outcomes appear to be similar to insulin for patients who achieve equal level of glycemic control. Alternately, metformin can be used in the second and third trimester. Patients on metformin will often require the addition of insulin to achieve glycemic goals. Limited studies of acarbose have suggested a possible role although safety data is limited and abdominal cramping may limit efficacy. Older sulfonylureas and the thiazolidinedione medications are not currently recommended in pregnancy.

Blood Sugar Monitoring

As noted, insulin dosing should be based on the results of blood glucose monitoring. For this reason, frequent finger-stick glucose monitoring should be a part of the management of patients treated with insulin. Although glycosylated hemoglobin values may provide adjunctive data concerning the level of glucose control, the long-term (3-month) retrospective nature of such testing makes it unsuitable for insulin management in pregnancy. Patients should be counseled to test blood sugar fasting and 2 h after every meal on a daily basis. If such intense monitoring is not feasible, patients should be counseled to vary daily (e.g., fasting and 2 h after lunch one day, 2 h after breakfast and 2 h after dinner the next) to allow for adequate assessment of insulin needs. Additional testing may be recommended at times when patients feel the symptoms of hypoglycemia to document the decrease in glucose levels.

Gestational Diabetes

Preconception Management

Preconception management of GDM begins with assessment of risk factors for the development of diabetes during pregnancy. The risk factors for GDM are listed in Table 15.1. All patients should be screened for risk factors for GDM. Patients found to be at increased risk may benefit from preconceptual diabetes testing as type 2 DM and GDM share common risk factors. Patients discovered to have diabetes prior to becoming pregnant should receive additional preconception counseling as noted earlier.

Management in Pregnancy

Patients with GDM should be managed similarly to those patients with pre-existing diabetes. Although many patients with GDM can be appropriately managed with lifestyle modification alone, all patients should be counseled concerning the indications for further treatment with insulin if necessary. All patients with diabetes should test blood sugar regularly to assess the adequacy of their treatment regimen.

Because of the fetal risks associated with diabetes in pregnancy, all patients with diabetes should begin fetal surveillance in the third trimester of pregnancy. Antenatal assessment is discussed in Chap. 18. In addition, because of the risk of macrosomia, careful assessment of fetal growth should be included in prenatal assessment. Patients with evidence of macrosomic or small-for-gestational-age fetuses should receive ultrasonographic assessment of fetal growth.

Management in Labor

During labor, efforts should be made to maintain the patient’s serum glucose levels between 80 and 110 mg/dL. Care should be taken, however, not to induce maternal hypoglycemia in patients who are restricted from eating or drinking during the course of labor. This is especially true for patients with prolonged second-stage labor.

Postpartum Management

All patients diagnosed with GDM should be screened for diabetes in the postpartum period to document resolution of the diabetes. Such patients are at increased risk for subsequent diagnosis of type 2 diabetes.