(1)
Department of Family Medicine, University of California, Riverside, Riverside, CA, USA
Key Points
1.
Diabetes mellitus (DM) is defined as carbohydrate intolerance resulting from either insulin deficiency or insulin insensitivity.
2.
Exposure to elevated serum glucose is associated with increased risk for organogenic birth defects, macrosomic infants, shoulder dystocia, and birth trauma.
3.
Gestational diabetes is defined as glucose intolerance first recognized during pregnancy.
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
Duodenal and anorectal atresia |
Hydronephrosis |
Renal agenesis |
Neural tube defects |
Anencephaly |
Ventricular septal defects |
Aortic coarctation |
Transposition of the great vessels |
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
Family history of diabetes |
Family history of macrosomic infants |
Ethnicity |
Obesity |
Past history of gestational diabetes |
Past history of macrosomic infant |
Multigestation |
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.
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