Diabetes in pregnancy (GDM, T1DM, and T2DM): Clinical sciences

Diabetes in pregnancy is characterized by hyperglycemia during gestation. Diabetes that initially arises during pregnancy is called gestational diabetes mellitus, or GDM. GDM develops in at-risk patients due to worsening insulin resistance that occurs in the second and third trimesters. Individuals might also present to obstetric care with type 1 or type 2 diabetes, which is referred to as pregestational diabetes. All types of diabetes in pregnancy increase the risk of complications, including fetal macrosomia, shoulder dystocia, preeclampsia, and cesarean birth. Pregestational diabetes has additional risks of congenital malformations, spontaneous abortion, and stillbirth.

Your first step in evaluating a patient with a chief concern suggesting diabetes in pregnancy is to obtain a focused history. Start by determining if the patient has GDM or pregestational diabetes, and then review recent blood glucose measurements. Patients with diabetes in pregnancy usually check a fingerstick glucose four to five times daily, including fasting; postprandial, or after each meal; and sometimes at bedtime. Most patients keep a glucose log, or you can scroll through glucose readings on their glucometer. Target glucose levels include a fasting glucose of less than 95 and either a one-hour postprandial glucose of less than 140 or a two-hour postprandial glucose that’s less than 120.

Individuals with GDM who consistently achieve target glucose levels with diet and exercise have A1GDM. A1GDM is also called diet-controlled GDM because blood glucose levels are adequately controlled without medication.

During the antepartum period, a patient with A1GDM should continue previously prescribed lifestyle modifications, including a carbohydrate-controlled diet and 30 minutes of moderate-intensity aerobic exercise at least 5 days per week, such as walking 10 to 15 minutes after each meal. Advise the patient to continue self-monitoring of fasting and postprandial glucose levels to assess the response to lifestyle interventions. You can modify the frequency of glucose monitoring if a patient’s glucose remains well controlled with diet and exercise.

Because of the higher risk of fetal macrosomia and shoulder dystocia, you should assess fetal growth by ultrasound in the late third trimester. If the estimated fetal weight is 4,500 grams or greater, counsel the patient regarding the risks and benefits of a scheduled cesarean delivery to reduce the risk of birth trauma.

Patients with A1GDM should deliver from 39 to 40 and 6/7 weeks. Once the patient with A1GDM is admitted for delivery, check their initial glucose level and repeat as indicated. Most patients with A1GDM remain euglycemic throughout labor.

After delivery, hyperglycemia associated with both types of GDM frequently resolves. However, up to one-third of patients with GDM will have impaired glucose metabolism at postpartum screening. Therefore, all patients with GDM should undergo screening for diabetes at 4 to 12 weeks postpartum with a 2-hour oral glucose tolerance test. Even if hyperglycemia is not noted, patients with GDM are at risk for developing diabetes years later.

On the flip side, patients with GDM who don’t consistently achieve target glucose levels after lifestyle changes have A2GDM. A2GDM requires the addition of pharmacotherapy along with diet and exercise to maintain blood glucose at target levels.

Insulin is first-line therapy because it doesn’t cross the placenta and it can achieve tight metabolic control. Metformin is a second-line option, but it crosses the placenta, and the long-term effects after fetal exposure are unknown. Metformin is a reasonable choice for patients who decline, can’t afford, or are unable to safely administer insulin.

Patients with A2GDM should continue a carbohydrate-controlled diet and regular exercise. Additionally, individuals should monitor fasting and postprandial glucose so pharmacotherapy can be titrated to achieve target glucose levels. Suboptimal glucose control increases the risk of fetal demise. Therefore, all patients who require pharmacotherapy should undergo antepartum fetal surveillance, usually starting at 32 weeks of gestation.

As before, assess fetal growth by ultrasound in the late third trimester, and counsel the patient on the risks and benefits of elective cesarean birth if the estimated fetal weight is 4,500 grams or more. The timing of delivery for patients with A2GDM depends on the response of glucose levels to diet, exercise, and pharmacotherapy.