Experts agree that glucose control is of paramount importance for pregnant women with type 1 diabetes. Diabetes authorities set especially strict blood sugar targets for expecting mothers, recommending that they take their glycemic management to the next level – for the health of both mother and child.
Recent experiments with continuous glucose monitoring (CGM) technology have added significantly to our understanding of how blood sugar levels impact the health of the growing fetus.
This article will summarize the latest research on how glucose levels affect the risk of Large Gestational Age (LGA), a common complication experienced by newborns with diabetic mothers.
The Problem: Large Gestational Age
Mothers with type 1 diabetes are significantly more likely to give birth to infants with Large Gestational Age.
Large gestational age is a term doctors use to describe newborn babies that are significantly larger than average. Big babies can be perfectly healthy, but LGA does carry with it some enhanced risks. Some of these hefty newborns will experience issues including breathing problems, hypoglycemia, and jaundice. Because of their size, infants are somewhat more likely to suffer injuries during birth, and doctors may want to recommend a Cesarean section (C-section) delivery.
To put it simply, LGA babies are more likely to have a difficult first few days of life.
There’s some dispute about the long-term consequences of LGA. While some studies assert that these kiddos do not suffer health, developmental, or educational difficulties, others link LGA with long-term health issues, including obesity, cardiovascular disease, and type 2 diabetes.
What CGMs Teach Us About LGA
A new research article published in the journal Diabetes Care looks at maternal glucose control and LGA in unprecedented detail. A multinational team took a closer look at the results of two previous trials that equipped pregnant women with continuous glucose monitors, analyzing how blood sugar readings correlated with the likelihood that children would be born with large gestational age.
They learned that women that give birth to infants with LGA have a blood sugar level that is consistently about 10 mg/dL higher than women that do not, a gap that persists at all times of day, from 10 weeks of pregnancy up until the birth itself.
After week 10 of gestation, achieving “a mean glucose of ≤7 mmol/L (≤126 mg/dL) was associated with having a normal-sized infant.” An average blood glucose level of 126 mg/dL correlates to a 7.0 percent A1C.
Similar associations were found between LGA and time-in-range and time-above-range, especially in the middle of pregnancy, between weeks 10 and 34 of gestation.
Hyperglycemia and the Developing Child
The two groups of women – those that did give birth to an LGA baby, and those that did not – had equivalent blood sugar levels up until week 10. That’s when things changed, possibly due to the advancing development of organs, including the pancreas, in the unborn child: “By 12 weeks of gestation, the fetal pancreas can respond to maternal glucose by increasing endogenous insulin production.”
That’s right: the pancreas of the tiny 12-week fetus can sense high glucose levels in the blood shared by its mother and increase its own insulin levels. Remember that insulin is the hormone most responsible for allowing fat cells to store energy – this reaction can actually cause the tiny fetus to pack on fat. Actually, it gets even weirder: Through a mechanism called the “fetal glucose steal,” the hyperinsulinemic child will cause glucose to “flux” across the placenta.
It’s important to emphasize that these higher blood sugar readings from the pregnancies with LGA babies were probably not the “fault” of the mothers in question. Mothers of both LGA babies and of normal-sized babies had similar blood sugar numbers during the first 10 weeks of pregnancy, suggesting that there was “a large physiologic component to the glycemic changes, which mirror gestational changes in maternal insulin sensitivity.” Pregnancy is different for everyone, and that goes for insulin sensitivity changes too; some are bound to have greater diabetes management challenges than others.
The American Diabetes Association sets forth the glycemic guidelines that doctors in the USA rely upon. Currently, the ADA recommends that women who hope to become pregnant target an A1C of <6.5 percent. During pregnancy itself, they should lower their A1C target to <6 percent, although patients that struggle with hypoglycemia may relax their target to <7 percent. These low blood sugar targets have been demonstrated to reduce the incidence of multiple issues associated with maternal hyperglycemia, including congenital anomalies, preeclampsia, and macrosomia in addition to LGA.
Many women with type 1 diabetes struggle to meet these extra-stringent targets, especially because pregnancy can make glucose management a lot more difficult. Early pregnancy is marked by a rise in insulin requirements, and then a gradual fall. During the second trimester, insulin resistance can skyrocket, and women can expect to double their daily insulin use to keep their blood sugars in check. Many women fail to meet recommended glucose targets until nearly the end of pregnancy, when rising insulin resistance finally begins to level off.
We have an article that explores the details of glycemic management during pregnancy: Pregnancy with Diabetes: Your Guide to Each Trimester.
The CGM during Pregnancy
The authors of the new Diabetes Care article also argue strongly in favor of the use of the CGM in pregnancy to help assess and guide glycemic management.
Diabetes authorities still use A1C as the most important benchmark for type 1 diabetes because most of our high-quality studies on health outcomes, many of which were completed before the availability of reliable CGMs, use A1C. But it should be plain to see why A1C is suboptimal as a tool for glucose management: as a 3-month snapshot of blood sugar values, it is not nearly responsive enough to the rapid changes characteristic of pregnancy.
A 2017 study showed that the mere use of a CGM, which improved the time-in-range numbers of pregnant women, could cut the likelihood of LGA in half. It also reduced neonatal intensive care visits and reduced the average length of hospital stay by an entire day.
The official ADA recommendations acknowledge the usefulness of CGMs, but stress that they should be used for secondary monitoring and that old-fashioned finger pricks should still form the basis of glycemic management during pregnancy, especially before and after meals. Nevertheless, the ADA does publish official time-in-range targets:
Source: American Diabetes Association Professional Practice Committee; 15. Management of Diabetes in Pregnancy: Standards of Medical Care in Diabetes—2022. Diabetes Care 1 January 2022; 45 (Supplement_1): S232–S243. https://doi.org/10.2337/dc22-S015
The new article concludes that these time-in-range targets are likely to be effective in preventing LGA. But please note that “time-in-range” means something very different during pregnancy: an upper limit of 140 mg/dL, not 180 mg/dL.
Blood sugar control isn’t the only modifiable factor that predisposes unborn children to LGA. A 2017 study of the same issue identified three other potential contributors to excessive fetal weight gain:
Pre-pregnancy maternal obesity
Maternal weight gain during pregnancy
High maternal triglyceride levels
The authors concluded that “optimal management of type 1 diabetes in pregnancy” requires close attention to the mother’s metabolic health in addition to the best possible glycemic management.
In a new study, mothers with type 1 diabetes that gave birth to children with large gestational age (LGA) were found to have persistently higher blood sugar readings and lower time-in-range, beginning in the tenth week of pregnancy.
We can’t know for sure if these women would have prevented their newborns’ LGA if they were able to lower their blood sugar to recommended levels, but the results nevertheless underline the importance of optimal glycemic control during pregnancy.
The authors recommend early intervention and the use of continuous glucose monitoring in all pregnant women with type 1 diabetes, in order to reduce the risks of complications from hyperglycemia as much as possible.
These results should not be generalized to pregnant women with type 2 diabetes or gestational diabetes.