Diabetes mellitus is the collective name for heterogeneous disturbances of metabolism which all are characterized by chronic hyperglycemia. In essence, there are three different types. While type I is caused by a disturbed secretion of insulin, type II and gestational diabetes are characterized by a disturbed action of insulin. Both causes can also occur simultaneously.
A poor glyccmic control in prcgestational diabetes, as measured by glycosylated hemoglobin (HbAlc > 6.5%), is correlated with an increased risk of major congenital malformations. HbAlc is a parameter for the blood glucose concentration of the last 120 days, the survival time of erythrocytes; it can also be referred to as the "blood sugar memory". The higher the concentration of HbAlc, the higher the statistically confirmed rate of malformations: an HbAlc of 8.5% is correlated with a malformation rate of 4%; an HbAlc of 10.5% has a risk for abnormalities of 6%. The most common birth defects are anomalies of the spine and extremities, of the heart and circulatory system, and neural tube defects. Urogenital defects, gastrointestinal fistulas, and atresias arc seen more seldom (for an overview, see Briggs 2005, Loft'redo 2001).
During pregnancy, women with all types of diabetes, as well as their infants, are at increased risk for a number of different complications: the miscarriage rate is increased, the perinatal morbidity is above average, and the rate of prematurity is almost 20% (Arbeitsgemeinschaft 2004, Gamson 2004). Characteristics of neonatal morbidity include macrosomia (an extremely large newborn) with immature organ functions or hypotrophy, and postpartum metabolic derangements of the newborn - especially hypoglycemia.
Pre-existing diabetes may be associated with vascular disease, leading to uteroplacental insufficiency and hypertensive disorders, resulting, for example, in prc-eclampsia.
The vast majority of type II or gestational diabetes occurs within the bounds of metabolic syndrome X (obesity, hyperlipidemia, hypertension, impaired glucose tolerance). In the beginning, there is insulin resistance of the insulin-dependent tissues. Therefore, an elevated insulin concentration is necessary for utilization of glucose. Hyperinsulinemia again intensifies the feeling of being hungry, which results in eating more and more, which leads to further weight gain, and so on - a vicious circle. Weight reduction results in lower insulin levels, and an increasing sensibility and amount of insulin receptors. Ideally, a body mass index of 27 kg/m2 and below should be achieved prior to pregnancy! Regarding the risk of pre-existing obesity for a pregnancy, see Chapter 2.5.
Achieving and maintaining euglycemia throughout gestation is the aim of diabetes therapy, because diabetic fetopathy appears to be due to fetal hyperglycemia and hyperinsulinemia, secondary to maternal hyperglycemia. Fetal hyperinsulinemia leads to hyperplasia and hypertrophy of islet cells, and increases the risk of respiratory distress syndrome (RDS). Children of mothers with insufficient blood sugar control during pregnancy have an increased risk of becoming obese during puberty or in early adulthood, or of developing diabetes or an imbalanced glucose tolerance.
Being overweight and gestational diabetes are steadily increasing in industrial countries: it is estimated that approximately 20% of pregnancies in overweight women are complicated by gestational diabetes. Therefore, the recommendation is to have a glucose tolerance test at least once in every pregnancy.
Insulin action changes during the course of pregnancy. At 10-14 weeks' gestation, insulin sensitivity is slightly increased; however, it then declines for the rest of the pregnancy, with insulin resistance being highest late in the third trimester. Insulin sensitivity rebounds with the delivery of the placenta. In cases of pre-existing diabetes, these changes contribute to a degree of hypoglycemia in the first trimester and increased insulin requirements during later pregnancy, and reinstitution of the pre-pregnancy insulin requirement after delivery.
Recommendation. Maintaining euglycemia throughout pregnancy is the best prerequisite for an uncomplicated course of pre- and postnatal development of the child, and for minimal maternal morbidity. This aim should ideally be achieved prior to pregnancy. Pregnant women with diabetes - no matter what type - should consult a specialist, if possible, and deliver in a perinatal center. All pregnant women should be screened for a diabetic metabolic disorder, especially if they are obese. An anatomical ultrasound and a-fetoprotein screening should be considered, especially for patients who are not euglycemic.
Was this article helpful?