By Nicole Recine RN, MSN, AGPCNP-BC
What Causes Gestational Diabetes? Why Do Women Without Diabetes Develop Gestational Diabetes During Pregnancy?
The prevalence of GDM seems to be increasing along with the rising rates of Type 2 Diabetes and Metabolic Syndrome in the general population. What causes diabetes to occur during pregnancy in women who have otherwise never had issues with blood sugar?
GDM is thought to manifest in women who already have underlying, chronic insulin resistance prior to becoming pregnant. In late pregnancy, there is a significant increase in fetal growth and demand for nutrients. To accommodate this demand, metabolic alterations occur to ensure that the growing fetus has ample nutrients to grow and develop. These adaptations are largely driven by increases in diabetogenic hormones such as growth hormone, cortisol, human chorionic somatomammotropin (HCS) and corticotropin-releasing hormone.
One result of this process is that the mother’s body develops a state of physiological insulin resistance where her body switches from primarily using carbohydrate for fuel to using fat for fuel. This allows more of the available glucose to be used to feed the growing fetus. The mother’s body becomes “resistant” to the action of insulin, which normally moves glucose into her cells to be used for energy. Her body instead runs on fat and ketones while glucose is shunted towards the growing fetus. To help facilitate this process, the placenta allows glucose, amino acids, and ketones to be transferred to the fetus but does not allow large fats to cross over so they can be spared for the mother. This is a normal and healthy adaptation that occurs during the second and third trimester of pregnancy. In this state, insulin levels are high and fasting blood glucose levels are lower than normal since much of the blood sugar is being directed to the fetus.
In healthy women, this physiological insulin resistance is not problematic. However, in women with underlying insulin resistance, these changes can push them over into a state of overt diabetes with insulin resistance above and beyond what is normal during pregnancy. This is when blood glucose levels rise and GDM is diagnosed. In a sense, pregnancy “unmasks” the chronic insulin resistance that may have been present for years. Further, while blood glucose levels may return to normal after pregnancy, the chronic, underlying insulin resistance still remains. If left untreated, this will often lead to Type 2 Diabetes, which explains why women who are diagnosed with GDM are at a higher risk for developing Type 2 diabetes later in life .
GDM is not only harmful to the mother but also significantly impacts the health of the fetus. In the short term, the fetus is at risk for macrosomia (high birth weight), hypoglycemia, birth trauma, and cardiac abnormalities. In the long term, being exposed to excessive levels of insulin and glucose in the womb predisposes the baby to obesity and Type 2 Diabetes later in life.
How is GDM diagnosed?
There are several ways to diagnose GDM. Methods and diagnosis thresholds can vary widely depending on the preferences of the provider.
The Two Step Approach: Most commonly used
Step 1: Screening
- The patient is given a 50-gram oral glucose load (fasting not required). Plasma or serum glucose is measured after one hour (not finger stick). If the patient’s blood glucose is greater than or equal to 135 mg/dL (cutoffs may vary by provider), a 100-gram oral glucose tolerance test will be administered in step 2.
Step 2: 100-gram oral glucose tolerance test
- The patient is given a 100-gram oral glucose tolerance test. This test involves measuring the fasting serum glucose, administering a 100-gram glucose load, and then measuring the glucose at one, two, and three hours after. Two or more elevated readings is positive for GDM.
The One Step Approach:
Step 1: 75-gram, two-hour, oral glucose tolerance test
- This method eliminates screening patients with the initial 50-gram glucose challenge. The patient must be fasting for this test. Serum blood glucose greater than or equal to 180 mg/dL at one hour or 152 mg/dL at two hours is diagnostic of GDM (cut offs may vary by
What does this mean for you?
If you have had GDM in the past, it may be a clue that you have underlying insulin resistance, even though your blood glucose levels are now normal. A diagnosis of Type 2 Diabetes is preceded by a (usually) long period of insulin resistance where insulin levels are elevated and blood glucose remains normal. If you have a history of GDM along with other markers of metabolic syndrome, a low carb, ketogenic approach may be worth considering.
Read more of Nicole Recine’s health & wellness articles on our Discover Blog.
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