The HbA1c test provides a picture of average blood glucose levels over the preceding two to three months. It measures the percentage of hemoglobin—a protein in red blood cells—that has become coated with sugar, a process called glycation. This measurement offers a broader view of blood sugar management compared to daily glucose tests, which only provide a snapshot. For this reason, it is a standard tool for monitoring long-term glucose control.
Target HbA1c Levels During Pregnancy
Managing blood glucose is a focus during pregnancy, with recommended HbA1c targets that are stricter than those for the general population. Before conception and during the first trimester, the goal for women with pre-existing diabetes is an HbA1c below 6.1% (43 mmol/mol). This tight control from the earliest stages of pregnancy is important to support healthy fetal development.
These lower targets are in place for specific physiological reasons. During pregnancy, hormonal shifts can lead to greater insulin resistance, making it more difficult for the body’s cells to absorb glucose. Additionally, the lifespan of red blood cells shortens, which can naturally lead to lower HbA1c readings. A healthcare provider may adjust specific goals based on an individual’s health to avoid problematic hypoglycemia.
The emphasis on HbA1c is most pronounced in the first trimester, after which its utility for monitoring diminishes. Healthcare teams then rely more on frequent self-monitoring of blood glucose levels. These daily checks provide real-time data that is more reflective of the rapid metabolic changes in the second and third trimesters. Post-pregnancy, the recommended HbA1c target returns to a level of 6.5% (48 mmol/mol) or below.
Distinguishing Between Gestational and Pre-existing Diabetes
The role and interpretation of the HbA1c test differ depending on whether a person has pre-existing diabetes (Type 1 or Type 2) or develops gestational diabetes. For women with pre-existing diabetes, HbA1c is used before conception to assess readiness for pregnancy and at the initial booking appointment to determine risk. Monthly HbA1c tests may be recommended before and during the first trimester to monitor glucose control.
In contrast, HbA1c is not the primary tool for diagnosing gestational diabetes. This condition emerges later in pregnancy, between 24 and 28 weeks, as a result of hormonal changes that cause insulin resistance. Because HbA1c reflects a long-term average, it cannot capture the rapid onset of this condition. The standard for diagnosis is the oral glucose tolerance test (OGTT).
Although not used for diagnosis, an HbA1c test may be performed when gestational diabetes is first suspected. A high reading at this point could indicate that a woman had undiagnosed type 2 diabetes before becoming pregnant. However, because pregnancy itself can lower HbA1c levels, the test can sometimes underestimate glucose intolerance, making the OGTT a more reliable diagnostic measure.
Health Implications of Elevated HbA1c
Elevated HbA1c levels during pregnancy carry health implications for both the mother and the developing fetus. For the mother, poorly controlled blood glucose increases the risk of developing preeclampsia, a condition characterized by high blood pressure. It also raises the likelihood of having a large baby (macrosomia), which can complicate delivery and increase the need for a C-section.
The risks for the infant are directly linked to the mother’s glucose levels, particularly during the first trimester when major organs are forming. An elevated HbA1c at this stage is associated with an increased risk of birth defects, especially those affecting the heart and central nervous system. If an HbA1c level is above 10%, women are advised to improve glucose control before becoming pregnant.
After birth, babies exposed to high glucose are at risk for several immediate health issues, including neonatal hypoglycemia (low blood sugar), breathing problems, and jaundice. Exposure to high glucose levels in utero is also linked to a higher risk of the child developing obesity or diabetes later in life.
Strategies for Managing HbA1c
Managing HbA1c levels during pregnancy involves a multi-faceted approach centered on lifestyle and medical intervention. Dietary management is a primary component. This involves working with a dietitian to create a meal plan that balances nutrient-dense carbohydrates, lean proteins, and healthy fats to prevent sharp spikes in blood glucose.
Regular physical activity, approved by a healthcare provider, is another part of management. Moderate exercise, such as walking for 30 minutes after a meal, helps regulate blood glucose levels. It also improves the body’s sensitivity to insulin, making it easier to maintain target glucose ranges.
Frequent self-monitoring of blood glucose is important for making timely adjustments to diet, activity, and medication. For women requiring medication, insulin is the preferred treatment, though metformin may be considered. Continuous glucose monitoring (CGM) systems can also be used, providing real-time data to help achieve tight glucose control while minimizing hypoglycemia risk.