Management of Diabetes during Pregnancy

The American Diabetes Association defines gestational diabetes as diabetes diagnosed in the second or third trimester of pregnancy without overt diabetes prior to gestation  (ADA, 2019). Gestational diabetes in the United States is approximately 6% of all pregnant women (Deputy et al., 2018). This rate has been increasing, likely due to maternal age and obesity changes. African American, Hispanic American, Native American, Pacific Islander, and South or East Asian women have higher rates than white women. The American College of Obstetricians and Gynecologists (ACOG) states that a diagnosis of gestational diabetes mellitus generally requires two or more values to meet or exceed glucose thresholds. However, clinicians may choose to make the diagnosis based on one elevated value (CPB, 2018).

There are numerous risk factors for gestational diabetes. Some of these risks include:

• History of impaired glucose tolerance
• Impaired fasting glucose
• Gestational diabetes mellitus in a previous pregnancy
• Family history of diabetes
• Prepregnancy BMI >30 kg/mg
• Excessive gestational weight gain during the first 18 to 24 weeks
• Maternal age >30 years of age
• Previous unexplained perinatal loss or birth of a malformed infant

Additional risks include:

• Glycosuria at the first prenatal visit
• Previous birth of an infant 4500 g
• Elevated LDL or triglycerides
• Medical conditions associated with the development of diabetes, such as metabolic syndrome, polycystic ovary syndrome, current use of glucocorticoids, hypertension or cardiovascular disease, acanthosis nigricans, or a multiple gestation pregnancy (CPB, 2018)

However, 20% of women with gestational diabetes do not have any risk factors.

For women who are obese, losing more than 10 pounds may decrease the risk of gestational diabetes. Regular exercise, a healthy diet, and smoking cessation may all improve health and decrease the risk of diabetes (Zhang, 2015).

All women should undergo a glucose tolerance test. This test may be done as early as the first prenatal visit if there is a high risk of having diabetes. If early screening is not done or is negative, a woman should be screened at 24 to 28 weeks gestation. There are two different ways to test for gestational diabetes. The one-step approach is when the woman is given a 75-gram dose of glucose, then her blood glucose level is tested 2 hours later. The woman also must be fasting. The two-step approach is most often used. The woman does not have to be fasting. She gets a 50-gram dose of glucose and has her glucose tested 1 hour later. If her sugar is abnormal, she will need a 2nd test. The 2nd test is a 3-hour glucose tolerance test where the woman has a fasting blood sugar drawn, then takes a 100-gram dose of glucose and has her blood sugar drawn every hour for 3 hours. Two or more abnormal results would diagnose the woman with gestational diabetes. Glycated hemoglobin (A1C) is not a good indicator when diagnosing gestational diabetes. It may be used in early pregnancy to determine if the woman has pre-existing diabetes (CPB, 2018). 

The first line of treatment for gestational diabetes is diet. The American Diabetes Association (ADA) recommends a nutrition plan that provides adequate nutrition for mom and fetus while achieving normoglycemia. Caloric intake is important to ensure that the woman and fetus get enough nutrition, but monitoring carbohydrate intake is important to keep glucose levels normal. Appropriate weight gain is important and varies depending on the woman’s BMI. Moderate exercise is also recommended as part of a treatment plan for gestational diabetes (Lebrun, 2011).

Glucose monitoring in pregnancy is important to determine the need for medications and prevent complications. Generally, fasting and postprandial glucose monitoring are recommended. Depending on providers, the postprandial sugars may be done 1 or 2 hours after the meal. Target glucose levels are fasting blood glucose values < 95 mg/dL and postprandial blood glucose values < 140 mg/dL at 1 hour and < 120 mg/dL at 2 hours (CPB, 2018).

Medications used to treat gestational diabetes are insulin, metformin, or glyburide. ACOG recommends insulin as the treatment of choice. Many patients who begin oral therapy will require insulin. The insulin dose should be started at 0.7-1.0 units/kg daily, and the dosage should be divided into long-acting or intermediate-acting insulin (CPB, 2018). The Society for Maternal-Fetal Medicine (SMFM) believes that metformin is a safe and reasonable first line of treatment (SMFM, 2018).

For all women with poor glucose control on medication without co-morbidities, weekly fetal monitoring should begin at 32 weeks or earlier if other co-morbidities exist. There is no consensus for fetal monitoring for women well controlled through diet, but it should start at > 32 weeks and include amniotic fluid volume assessment due to the risk of polyhydramnios (CPB, 2018).

Women with gestational diabetes whose glucose is well controlled by diet should be delivered after 39 weeks and can wait up to 40 weeks 6 days with antepartum testing. A woman who is well controlled on medication should deliver at 39 weeks 0 days to 39 weeks 6 days. A woman with poorly controlled diabetes may be recommended to deliver between 37 weeks 0 days and 38 weeks 6 days, with delivery between 34 weeks 0 days and 36 weeks 6 days reserved for failure of in-hospital glycemic control or abnormal fetal testing. A patient with an estimated fetal weight ≥ 4500 should be counseled regarding a scheduled cesarean section (CPB, 2018). Women with gestational diabetes should be monitored during labor and maintain good glycemic control to prevent newborn hypoglycemia after delivery. 

Gestational diabetes can have serious consequences for the mother and the fetus. There is an increased risk of preeclampsia, polyhydramnios, macrosomia, maternal and infant birth trauma, operative delivery (cesarean, instrumental), and hypoglycemia (GPD, 2020). Good glycemic control can help to prevent these complications. Women with gestational diabetes also have an increased risk of developing diabetes later.

Women with pregestational diabetes should be well-controlled before getting pregnant with a planned pregnancy. Women with unplanned pregnancies should regulate their glucose as soon as possible. Women who have hemoglobin A1C levels of < 6 to 6.5 percent early in pregnancy have the lowest rates of fetal complications, such as miscarriage and congenital anomalies (CPB, 2018b).

Glucose monitoring for these women is similar to that of gestational diabetes. Fasting sugars, pre-prandial or postprandial sugars, and hemoglobin A1C levels are important for these women. Women with pregestational diabetes who are on oral treatment should be switched to insulin treatment, and women who were already on insulin will need a modification to their regimen (CPB, 2018b).

Women with pregestational diabetes should have renal function assessed throughout the pregnancy. These women are also at risk for thyroid dysfunction. Cardiac function may need to be monitored, and eye exams to monitor for retinopathy. Preeclampsia is also a concern, and low-dose aspirin may be prescribed to prevent it. 

Fetal risks include miscarriage and congenital malformations early in pregnancy. Neural tube defects and congenital heart disease are higher in this population. Fetal demise is rare due to increased surveillance and improved glycemic control for these women. Polyhydramnios is another risk for the fetus. An increased amount of amniotic fluid could cause complications such as a cord prolapse if the woman’s water breaks. 

Diabetic ketoacidosis is a life-threatening emergency that may occur probably due to increased insulin resistance. Symptoms of diabetic ketoacidosis may include abdominal pain, nausea and vomiting, and altered sensorium. Treatment includes hydration and intravenous insulin (CPB, 2018b).

Usually, weekly monitoring begins at 32 weeks, although this may begin earlier and increase to twice weekly at 36 weeks gestation. Fetal growth is monitored closely because these fetuses may grow large for gestational age (LGA). LGA fetuses increase the risk of long labor, shoulder dystocia, operative delivery, maternal and infant birth trauma, and perinatal death (CPB, 2018b). The newborn is at risk for hypoglycemia. Preterm labor is also a higher risk. Fetuses born prior to 34 weeks, whether due to preterm labor or a planned early delivery, should receive glucocorticoids to promote fetal lung maturity.

ACOG recommends delivery at 39 weeks 0 days to 39 weeks 6 days. A woman with poorly controlled diabetes or vascular disease should deliver between 36 weeks 0 days and 38 weeks 6 days (CPB, 2018b). Women with pregestational diabetes also require strict glycemic control during labor. A titratable insulin drip with frequent glucose monitoring is usually recommended for good control.