Gestational diabetes
Physiology
Pregnancy is a “diabetogenic state” with increased insulin resistance and reduced peripheral uptake of glucose (due to placental hormones with anti-insulin activity). In this way, the fetus has a continuous supply of glucose.
Incidence
Three to five percent of pregnancies.
Maternal complications
- Gestational diabetes poses little risk to the mother. Such women are not at risk of diabetic ketoacidosis (DKA), which is a disease resulting from an absolute deficiency of insulin.
- Care should be taken to avoid iatrogenic hypoglycemia due to excessive insulin administration.
- Gestational diabetes is a good screening test for insulin resistance; 50% will develop gestational diabetes in a subsequent pregnancy, and 40–60% will develop diabetes later in life.
Fetal complications
Fetuses of women with poorly controlled gestational diabetes are exposed to high concentrations of glucose and, as a result, grow large. Fetal macrosomia (see Chapter 51) is associated with an increased risk of cesarean section delivery and birth injury (see Chapter 63).
Screening
- Glucose load test (GLT) is used to screen for gestational diabetes. In the UK, screening is recommended only for high-risk women at approximately 28 weeks. Risk factors include women with a family history of diabetes, sustained glycosuria, obesity, or a history of gestational diabetes, fetus macrosomia, or unexplained fetal demise. US practice favors screening all pregnant women at 24–28 weeks, and high-risk women in the first trimester at 16–20 weeks and again at 24–28 weeks.
- GLT is a non-fasting test, but women should not eat after their 50-g glucose load until a venous blood sample is drawn 1 hour later. A positive test should be followed by a glucose tolerance test
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