White’s classification of diabetes in pregnancy.

Dr. Priscilla White, a physician who worked with pregnant women with diabetes during the 1940s, developed a classification system specifically for use with this group of women (Table 20-1). Dr. White’s system was based on age at diagnosis, duration of illness, and presence of vascular disease (Landon et al., 2007; Moore & Catalano, 2009). Her classification system has been modified through the years but is still frequently used today to assess both maternal and fetal risk. Women in classes A through C generally have good pregnancy outcomes as long as their blood glucose levels are well controlled. Women in classes D through T, however, usually have poorer pregnancy outcomes because they have already developed the vascular damage that often accompanies long-standing diabetes.

Preconception counseling

Preconception counseling is recommended for all women of reproductive age who have diabetes because it is associated with less perinatal mortality and fewer congenital anomalies (Moore & Catalano, 2009). Under ideal circumstances, women with pregestational diabetes are counseled before the time of conception to plan the optimal time for pregnancy, establish glycemic control before conception, and diagnose any vascular complications of diabetes. However, estimates indicate that fewer than 20% of women with diabetes in the United States participate in preconception counseling (Landon et al., 2007).

The woman’s partner should be included in the counseling to assess the couple’s level of understanding related to the effects of pregnancy on the diabetic condition and of the potential complications of pregnancy as a result of diabetes. The couple should also be informed of the anticipated alterations in management of diabetes during pregnancy and the need for a multidisciplinary team approach to health care. Financial implications of diabetic pregnancy and other demands related to frequent maternal and fetal surveillance should be discussed. Contraception is another important aspect of preconceptional counseling to assist the couple in planning effectively for pregnancy.

Maternal risks and complications

Although maternal morbidity and mortality rates have improved significantly, the pregnant woman with diabetes remains at risk for the development of complications during pregnancy. Poor glycemic control around the time of conception and in the early weeks of pregnancy is associated with an increased incidence of miscarriage. Women with good glycemic control before conception and in the first trimester are no more likely to miscarry than women who do not have diabetes (Moore & Catalano, 2009).

Poor glycemic control later in pregnancy, particularly in women without vascular disease, increases the rate of fetal macrosomia. Macrosomia has been defined in several different ways, including a birthweight more than 4000 to 4500 g, birthweight above the 90th percentile, and estimates of neonatal adipose tissue. Macrosomia occurs in approximately 40% of pregestational diabetic pregnancies and in up to 50% of pregnancies complicated by GDM (Landon et al., 2007; Moore & Catalano, 2009). Infants born to mothers with diabetes tend to have a disproportionate increase in shoulder, trunk, and chest size. Because of this tendency the risk of shoulder dystocia is greater in these babies than in other macrosomic infants. Women with diabetes therefore face an increased likelihood of cesarean birth because of failure of fetal descent or labor progress or of operative vaginal birth (birth involving the use of episiotomy, forceps, or vacuum extractor) (Landon et al.; Moore & Catalano).

Women with preexisting diabetes are at risk for several obstetric and medical complications. In general the risk of developing these complications increases with the duration and severity of the woman’s diabetes. In one study the rates of preeclampsia, preterm birth, cesarean birth, and maternal mortality were much higher in women with preexisting diabetes than in women who did not have this disease. Approximately a third of women who have had diabetes for more than 20 years, for example, develop preeclampsia. Women with nephropathy and hypertension in addition to diabetes are also increasingly likely to develop preeclampsia. The rate of hypertensive disorders in all types of pregnancies complicated by diabetes is 15% to 30%. Chronic hypertension occurs in 10% to 20% of all diabetic pregnancies, and in up to 40% of those in women who have preexisting renal or retinal vascular disease (Moore & Catalano, 2009).

Hydramnios (polyhydramnios) occurs approximately 10 times more often in diabetic than in nondiabetic pregnancies. Hydramnios (amniotic fluid in excess of 2000 ml) is associated with premature rupture of membranes, onset of preterm labor, and postpartum hemorrhage (Cunningham, Leveno, Bloom, Hauth, Gilstrap, & Wenstrom, 2005).

Infections are more common and more serious in pregnant women with diabetes than in pregnant women without the disease. Disorders of carbohydrate metabolism alter the body’s normal resistance to infection. The inflammatory response, leukocyte function, and vaginal pH are all affected. Vaginal infections, particularly monilial vaginitis, are more common. Urinary tract infections (UTIs) are also more prevalent. Infection is serious because it causes increased insulin resistance and may result in ketoacidosis. Postpartum infection is more common among women who are insulin dependent.

Ketoacidosis (accumulation of ketones in the blood resulting from hyperglycemia and leading to metabolic acidosis) occurs most often during the second and third trimesters, when the diabetogenic effect of pregnancy is the greatest. When the maternal metabolism is stressed by illness or infection, the woman is at increased risk for diabetic ketoacidosis (DKA) DKA can also be caused by poor patient compliance with treatment or the onset of previously undiagnosed diabetes (Moore & Catalano, 2009). The use of beta-mimetic drugs such as terbutaline for tocolysis to arrest preterm labor may also contribute to the risk for hyperglycemia and subsequent DKA (Cunningham et al., 2005; Iams, Romero, & Creasy, 2009).

DKA may occur with blood glucose levels barely exceeding 200 mg/dl, as compared with 300 to 350 mg/dl in the nonpregnant state. In response to stress factors such as infection or illness, hyperglycemia occurs as a result of increased hepatic glucose production and decreased peripheral glucose use. Stress hormones, which act to impair insulin action and further contribute to insulin deficiency, are released. Fatty acids are mobilized from fat stores to enter into the circulation. As they are oxidized, ketone bodies are released into the peripheral circulation. The woman’s buffering system is unable to compensate, and metabolic acidosis develops. The excessive blood glucose and ketone bodies result in osmotic diuresis with subsequent loss of fluid and electrolytes, volume depletion, and cellular dehydration. DKA is a medical emergency. Prompt treatment is necessary to prevent maternal coma or death. Ketoacidosis occurring at any time during pregnancy can lead to intrauterine fetal death. The incidence of DKA during pregnancy has decreased to approximately 2% from a rate of 20% or more in the past. The rate of intrauterine fetal demise (IUFD) with DKA, formerly approximately 35%, is currently 10% or less (Moore & Catalano, 2009) (Table 20-2).

The risk of hypoglycemia (a less-than-normal amount of glucose in the blood) is also increased. Early in pregnancy, when hepatic production of glucose is diminished and peripheral use of glucose is enhanced, hypoglycemia occurs frequently, often during sleep. Later in pregnancy, hypoglycemia may also result as insulin doses are adjusted to maintain euglycemia (a normal blood glucose level). Women with a prepregnancy history of severe hypoglycemia are at increased risk for severe hypoglycemia during gestation. Mild to moderate hypoglycemic episodes do not appear to have significant deleterious effects on fetal well-being (see Table 20-2).

Fetal and neonatal risks and complications

From the moment of conception the infant of a woman with diabetes faces an increased risk of complications that may occur during the antepartum, intrapartum, or neonatal periods. Infant morbidity and mortality rates associated with diabetic pregnancy are significantly reduced with strict control of maternal glucose levels before and during pregnancy.

Despite the improvements in care of pregnant women with diabetes, intrauterine fetal demise (IUFD) (sometimes known as stillbirth) is still a major concern. Approximately 2% to 5% of all fetal deaths occur in women whose pregnancies are complicated by preexisting diabetes. Hyperglycemia, ketoacidosis, congenital anomalies, infections, and maternal obesity are thought to be reasons for fetal death. In the third trimester, fetal acidosis is the most likely cause of fetal death (Paidas & Hossain, 2009).

The most important cause of perinatal loss in diabetic pregnancy is congenital malformations, which account for 30% to 50% of all perinatal loss (Lindsay, 2006). The incidence of congenital malformations is related to the severity and duration of the diabetes. Hyperglycemia during the first trimester of pregnancy, when organs and organ systems are forming, is the main cause of diabetes-associated birth defects. Anomalies commonly seen in infants affect primarily the cardiovascular system, the CNS, and the skeletal system (Cunningham et al., 2005; Moore & Catalano, 2009) (see Chapter 24).

The fetal pancreas begins to secrete insulin at 10 to 14 weeks of gestation. The fetus responds to maternal hyperglycemia by secreting large amounts of insulin (hyperinsulinism). Insulin acts as a growth hormone, causing the fetus to produce excess stores of glycogen, protein, and adipose tissue and leading to increased fetal size, or macrosomia. Birth injuries are more common in infants born to mothers with diabetes compared with mothers who do not have diabetes and macrosomic fetuses have the highest risk for this complication. Common birth injuries associated with diabetic pregnancies include brachial plexus palsy, facial nerve injury, humerus or clavicle fracture, and cephalhematoma. Most of these injuries are associated with difficult vaginal birth and shoulder dystocia (Moore & Catalano, 2009). Hypoglycemia at birth is also a risk for infants born to mothers with diabetes (for further discussion of neonatal complications related to maternal diabetes, see Chapter 24).