Approach to diabetes in pregnancy: Clinical sciences

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Introduction0:00–1:12

Diabetes is one of the most common medical complications in pregnancy. Patients with diabetes in pregnancy are more likely to develop preeclampsia and undergo cesarean delivery.
Additionally, higher glucose levels cross the placenta, resulting in an increased glucose supply to the fetus. The fetal pancreas responds by producing more insulin to handle the excess glucose.
Fetal hyperinsulinemia promotes increased fat accumulation, particularly in the shoulders and chest, that can cause macrosomia; shoulder dystocia; and birth trauma.
Moreover, once the umbilical cord is clamped after delivery, the maternal glucose supply is interrupted, which can lead to neonatal hypoglycemia.
Most cases of diabetes in pregnancy are gestational diabetes mellitus, or GDM, which is hyperglycemia that develops during pregnancy.
However, many patients don’t receive diabetes screening before pregnancy, so it can be challenging to differentiate between GDM and previously existing, or pregestational, type 1 or type 2 diabetes.
The first step in evaluating a patient who presents for diabetes screening in pregnancy is to obtain a focused history and physical exam, ideally at the initiation of prenatal care.

History and Physical exam1:12–2:58

First, you want to assess whether a patient has a previous diagnosis of either type 1 or type 2 diabetes. If they do, that’s pregestational diabetes mellitus.
This is an important distinction to make, because patients with pregestational diabetes are more likely to have significant maternal and fetal complications during pregnancy, and usually require additional monitoring.
On the flip side, if your patient has no previous diagnosis of type 1 or type 2 diabetes, your next step is to assess whether they’re at high risk for GDM.
A patient who is at high risk will have an elevated BMI of at least 25, or at least 23 in patients of Asian descent; plus one or more additional risk factors.
These additional risk factors in history include GDM in a previous pregnancy; a first-degree relative with diabetes; previous delivery of an infant weighing at least 4,000 grams or about 9 pounds; or a personal history of polycystic ovarian syndrome or cardiovascular disease.
Some additional risk factors can be discovered on physical examination, including hypertension, or prepregnancy morbid obesity with a BMI greater than 40.
Finally, additional risk factors related to labs include a hemoglobin A1c of 5.7 % or greater, and certain abnormal lipid values, like an HDL lower than 35 mg/dL and triglycerides higher than 250 mg/dL.
All pregnant patients should be screened for GDM - it’s just a matter of when, which is based on assessment of risk factors.

Average risk for GDM2:58–6:01

First, let’s talk about patients who are at “average risk” for GDM; meaning they have no additional risk factors for GDM.
Average risk patients are screened at 24 to 28 weeks of gestation with a 50-gram, one-hour oral glucose tolerance test. A normal test result indicates that the patient does not have gestational diabetes and can proceed with routine prenatal care.
Here’s a clinical pearl! The cut-off value for a normal one-hour glucose test varies between 130 and 140 mg/dL because there isn’t enough evidence to determine the ideal threshold to screen for gestational diabetes.
Each clinical site or institution should decide which cut-off to use for screening and remain consistent throughout their practice.
Alright, whichever screening cut-off is used, if the one-hour glucose test for an average-risk patient is elevated, the patient should then undergo a 100-gram, three-hour oral glucose tolerance test.
This test includes a fasting glucose measurement as well as additional measurements at 1, 2, and 3 hours after consuming the glucose load.Here’s a high-yield fact!
A commonly used set of diagnostic thresholds for the three-hour glucose test is the Carpenter and Coustan criteria, which include normal glucose values of fasting below 95, a one-hour result below 180, a two-hour result below 155, and a three-hour result below 140.
Another acceptable approach would be to use glucose values established by the National Diabetes Data Group, which are fasting less than 105, a one-hour less than 190, a two-hour less than 165, and a three-hour less than 145.
Okay, back to our patient. The three-hour test is considered normal if no more than one of the four values is elevated.
A normal 3-hour test result at 24 to 28 weeks means that your patient does not have gestational diabetes and can resume routine prenatal care.
Here’s another clinical pearl! Patients with only one elevated value on a three-hour glucose tolerance test are considered to have a normal result, but are still diagnosed with impaired glucose tolerance.
This means they still have a significantly increased risk of adverse pregnancy outcomes, including neonatal macrosomia, compared to those with no abnormal values on the test, and may benefit from closer observation.
Now, if the three-hour glucose tolerance test has two or more elevated glucose measurements, the test result is abnormal, and you have diagnosed your patient with gestational diabetes.And another quick clinical pearl!
There’s also a one-step 75-gram glucose tolerance test, which does both the screening and the diagnosis, but this is less preferred over the two-step 50- and 100-gram test.Okay, before we move on to classification, let’s go back to our risk assessment and talk about patients who are at high risk for GDM.
These patients should undergo screening at the initiation of prenatal care with an early one-hour oral glucose tolerance test.
If the patient’s early one-hour glucose test is normal, they can return to routine average-risk GDM screening at 24 to 28 weeks.
However, if the early one-hour glucose test is elevated, then the patient should proceed with an early three-hour oral glucose tolerance test.

High risk for GDM6:01–7:54

An abnormal early three-hour test means your patient has gestational diabetes. Now, if your patient has a normal early three-hour oral glucose tolerance test, they should be retested at 24 to 28 weeks.
However, at that time, you can skip the one-hour test for these patients because patients with an abnormal early one-hour glucose screen are likely to have an abnormal one-hour screen later in the pregnancy.
So, go directly to the three-hour test at 24 to 28 weeks. If it’s abnormal, the patient has developed gestational diabetes.
But, if it’s normal, they can continue routine prenatal care.Here’s a clinical pearl! In the past, when a clinician diagnosed diabetes at any point in pregnancy, it was considered GDM even though some of these patients actually had pregestational diabetes.
Today if you identify diabetes in the first trimester or early second trimester with the standard diagnostic criteria of a hemoglobin A1c of 6.5% or greater, a fasting glucose of 126 or greater, or a 2-hour glucose of 200 or greater on a 75-gram oral glucose tolerance test, you can diagnose pregestational diabetes.
Now that you have made the diagnosis of gestational diabetes mellitus, let’s talk about how to classify it. Patients diagnosed with gestational diabetes should receive education on lifestyle modifications, including nutritional counseling for a carbohydrate-controlled diet as well as safe, regular exercise.
Patients should also learn to check fasting and postprandial, or after-meal, fingerstick glucose levels daily to assess the response of glucose control to lifestyle interventions.
Target glucose levels include a fasting glucose of less than 95 mg/dL and either a one-hour postprandial glucose of less than 140 mg/dL or a two-hour postprandial glucose that’s less than 120 mg/dL.

Gestational diabetes mellitus7:54–9:19

Clinicians typically review a patient’s glucose levels every 1 to 2 weeks. Patients who are able to consistently achieve target glucose levels with diet and exercise alone have A1GDM, and can continue their current management.
On the other hand, those who are not able to consistently achieve target glucose levels have A2GDM and require a combination of diet, exercise, and medication for optimal management.
So, you should add pharmacotherapy, typically insulin, to achieve adequate glucose control. Metformin is a reasonable second-line choice for patients who decline, can’t afford, or are unable to safely administer insulin.
Alright, as a quick recap… Diabetes mellitus is a common medical complication of pregnancy. Some patients enter pregnancy with a previous diagnosis of type 1 or type 2 diabetes, called pregestational diabetes; but most of the time you’ll diagnose diabetes in pregnancy with early or routine glucose screening for gestational diabetes mellitus.
Patients at average risk for GDM undergo glucose screening at 24 to 28 weeks. Patients at high risk for GDM should begin screening at the initiation of prenatal care.
Individuals who are diagnosed with GDM should receive education on a carbohydrate-controlled diet and safe, regular exercise as well as how to check fasting and postprandial glucose measurements.
Those who are able to control their glucose levels this way have A1GDM. However, if they cannot consistently achieve target glucose levels after lifestyle modifications, they have A2GDM and need pharmacotherapy for management.

Review9:19–10:18

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