A new study has shown that despite excellent glycemic control and low glycemic variability throughout their pregnancies, women with type 1 diabetes tended to give birth to infants who were large for gestational age. To examine trimester-specific associations among glycemic variability, fetal growth, and birthweight in pregnancies with type 1 diabetes mellitus (Type 1 DM).

Researchers documented elevated fetal weight and abdominal circumference percentages throughout the pregnancies that were consistent with accelerated prenatal growth. The study was published in Diabetes Technology & Therapeutics (DTT).

Glycemic Variability

Researchers used continuous glucose monitoring (CGM) to determine glycemic variability over a 7-day period in each trimester of the women's pregnancies. In the article entitled "Continuous Glucose Monitoring, Glycemic Variability, and Excessive Fetal Growth in Pregnancies Complicated by Type 1 Diabetes" the researchers reported mean HbA1c of 6.5%, 6.1%, and 6.4% during the first, second, and third trimester, respectively.

"Fetal macrosomia continues to be a problem in patients with type 1 diabetes associated with the pregnancy despite improvements in overall glucose control. With the availability of a hybrid-closed loop system, it will be important to see if fetal overweight can be reduced with automatic delivery of insulin based on sensor glucose values," says DTT Editor-in-Chief Satish Garg, MD, Professor of Medicine and Pediatrics at the University of Colorado Denver (Aurora).

Hyperglycemia

Although maternal hyperglycemia is a key pathway associated with fetal overgrowth, factors other than glycemic control may contribute to LGA. We previously reported that third-trimester maternal placental growth factor levels were predictive of birthweight, independent of HbA1c. 

Diabetes

These data, together with the low rate of diabetes complications in our study population, point to the possibility that this contemporary group of women with Type 1 DM has better vascular function and placental blood flow than historical controls.

The occurrence of LGA remains very high in contemporary U.S. women with Type 1 DM, despite the use of CGM and overall good glycemic control. Neither HbA1c nor glycemic variability predicted fetal overgrowth or birthweight.

Since LGA is a key driver of maternal and newborn complications in pregnancies with Type 1 DM, our data emphasize the importance of investigating both glucose-dependent and glucose-independent underlying mechanisms.