Insulin is a naturally occurring hormone that allows glucose, or sugar, to move from the bloodstream into the body’s cells for energy. When the body cannot produce or effectively use its own insulin, blood sugar levels rise, posing risks during pregnancy for both the mother and the developing fetus. Because insulin does not cross the placenta, it is the safest and preferred method for managing high blood sugar levels throughout gestation. Achieving tight glucose control reduces the risks of complications like preeclampsia, fetal overgrowth (macrosomia), and neonatal hypoglycemia after birth.
Choosing and Preparing Insulin
Insulin therapy in pregnancy typically involves two main categories: basal and rapid-acting insulin. Basal, or long-acting, insulin works over many hours to cover the body’s background glucose needs between meals and overnight. Rapid-acting insulins, such as insulin aspart and insulin lispro, are taken at mealtimes to manage the spike in blood sugar that follows carbohydrate consumption.
Unopened insulin pens or vials must be stored in the refrigerator, but freezing destroys the medication. Once opened, insulin can be safely stored at room temperature for a limited period, often 28 to 42 days, depending on the specific type. Before each use, check the expiration date and ensure the liquid appears normal. Intermediate-acting insulin, like NPH, needs to be gently rolled between the palms to mix the cloudy suspension before injection.
The medication is commonly delivered via pre-filled pens or syringes, requiring a new, sterile needle for every injection. Before dialing the prescribed dose on an insulin pen, a small “air shot” (priming) of two units should be performed. This ensures the needle is clear and confirms the correct dose will be delivered subcutaneously, just under the skin.
Proper Injection Technique and Timing
For safe and effective delivery, insulin must be injected into the fatty tissue layer beneath the skin, not into muscle, which causes erratic absorption and pain. Acceptable injection sites during pregnancy include the abdomen, thighs, upper arms, and upper buttocks. When using the abdomen, inject at least two inches away from the belly button and avoid areas where the skin may be overly taut in later pregnancy.
Site rotation involves using a different spot for each injection, ensuring each new injection is about one inch away from the last. Failing to rotate sites can lead to small, firm lumps called lipohypertrophy, which impair insulin absorption and affect glucose control. Washing hands with soap and water before handling the equipment helps prevent infection at the injection site.
The injection is typically administered at a 90-degree angle, pushing the needle straight into the skin. The skin should not be pinched unless directed by a healthcare provider. After the plunger is fully depressed or the pen’s dose counter returns to zero, hold the needle in place for a slow count of ten before withdrawal.
Correct timing of rapid-acting insulin relative to a meal is necessary for optimal post-meal control, generally requiring injection within 15 minutes before or right after starting to eat. Used needles must be removed immediately and disposed of safely in a dedicated sharps container to prevent accidental needle-stick injuries.
Adjusting Insulin Doses Throughout Gestation
The body’s need for insulin changes significantly throughout pregnancy due to shifting hormone levels. During the first trimester, some individuals experience a temporary increase in insulin sensitivity, which can lead to a slight decrease in required insulin dosage. This enhanced sensitivity is often short-lived and increases the risk of low blood sugar events.
The second and third trimesters are characterized by a dramatic increase in insulin resistance, primarily driven by placental hormones like human placental lactogen (HPL). These hormones interfere with insulin action, requiring injected insulin to work harder to keep blood sugar levels within the target range. Insulin requirements can increase by as much as two to three times the pre-pregnancy dose by the final trimester.
To maintain tight glucose control, frequent adjustments are necessary. Target levels include a fasting blood sugar below 95 mg/dL and a one-hour post-meal level below 140 mg/dL. This requires diligent and frequent blood glucose monitoring (BGM) throughout the day. Communication with the healthcare team is necessary for dose titration, often requiring weekly or daily changes to the insulin regimen.
A significant drop in insulin requirements late in the third trimester can signal placental dysfunction and warrants immediate medical evaluation. Following delivery, the removal of the placenta causes an immediate decrease in insulin resistance. Doses typically drop back to near pre-pregnancy levels very quickly, and the healthcare team will adjust the insulin dose substantially right after birth to prevent severe hypoglycemia.
Managing Hypoglycemia and Hyperglycemia
The use of insulin requires constant vigilance for both hypoglycemia (low blood sugar) and hyperglycemia (high blood sugar). Hypoglycemia is defined as a blood sugar level below 70 mg/dL and can manifest with symptoms like shaking, sweating, confusion, and a fast heartbeat. Treating a mild to moderate low blood sugar episode immediately prevents it from worsening.
The “Rule of 15” provides a protocol for treating a low: consume 15 grams of a fast-acting carbohydrate, such as four ounces of juice or three to four glucose tablets. Recheck the blood sugar after 15 minutes, and repeat the process if the level remains below 70 mg/dL. Once corrected, consuming a small snack containing protein and a longer-acting carbohydrate helps stabilize blood sugar.
Hyperglycemia, or high blood sugar, is also a concern; symptoms often include increased thirst and frequent urination. Persistent high blood sugar levels negatively impact fetal development and increase maternal risk for complications. This should be addressed through dose adjustments guided by the healthcare provider. Consistent monitoring and adherence to the prescribed insulin and dietary plan are the best preventative measures.