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WASHINGTON — Continuous glucose monitoring (CGM) is widely used during pregnancy for individuals with type 1 diabetes — with pregnancy-specific target metrics now chosen and benefits on perinatal outcomes demonstrated — but more research is needed to elucidate its role in the growing population of pregnant people with type 2 diabetes and gestational diabetes (GDM). And overall, there are still “many more questions unanswered about CGM use in pregnancy than what we have answered,” Celeste Durnwald, MD, said at the biennial meeting of the Diabetes in Pregnancy Study Group of North America.
There’s much to learn about how to best interpret “the detailed and complex data that CGM provides,” and what targets in addition to time in range (TIR) are most important, said Dr. Durnwald, director of the perinatal diabetes program and associate professor of ob.gyn. at the Hospital of the University of Pennsylvania, Philadelphia, in a presentation on CGM.
Among other questions are whether fasting glucose is “as important in the era of CGM,” and whether there should be different glycemic targets for nocturnal versus daytime TIR, she said. Moreover, questions justifiably remain about whether the TIR targets for type 1 diabetes in pregnancy are indeed optimal, she said in a discussion period.
Ongoing research is looking at whether CGM can motivate and guide patients with GDM through diet and lifestyle changes such that “we can see changes in amounts of medication we use,” Dr. Durnwald noted in her presentation. “There’s a whole breadth of research looking at whether CGM can help predict diagnosis of GDM, large for gestational age, or preeclampsia, and what are the targets.”
Maternal hypoglycemia during pregnancy — a time when strict glycemic control is recommended to reduce the risk of congenital malformations and other fetal and neonatal morbidity — remains a concern in type 1 diabetes, even with widespread use of CGM in this population, said Barak Rosenn, MD, during a presentation on glycemic control in type 1 diabetes.
A pilot study of a newly designed pregnancy-specific closed-loop insulin delivery system, published last year (Diabetes Care. 2023;46:1425-31), has offered the first “really encouraging information about the ability to use our most up-to-date technology to help our type 1 patients maintain strict control and at the same time decrease their risk of severe hypoglycemia,” said Dr. Rosenn, a maternal-fetal medicine specialist at the Jersey City Medical Center, Jersey City, New Jersey.
Guidance for tight intrapartum glucose control, meanwhile, has been backed by little evidence, said Michal Fishel Bartal, MD, MS, and some recent studies and reviews have shown little to no effect of such tight control on neonatal hypoglycemia, which is the aim of the guidance.
“We need to reexamine current recommendations,” said Dr. Bartal, assistant professor in the division of maternal-fetal medicine at the University of Texas Health Science Center, Houston, during a presentation on intrapartum care. “There’s very limited evidence-based data for the way we manage people with diabetes [during labor and delivery].”
The Knowns And Unknowns of CGM in Pregnancy
The multicenter, international CONCEPTT trial (Continuous Glucose Monitoring in Pregnant Women With Type 1 Diabetes), published in 2017, was the first trial to demonstrate improvements in perinatal outcomes, and it “brought CGM to the forefront in terms of widespread use,” Dr. Durnwald said.
The trial randomized more than 300 patients with type 1 diabetes who were pregnant or planning pregnancy (both users of insulin pumps and users of multiple insulin injections) to continuous, real-time CGM in addition to finger-stick glucose monitoring, or standard finger-stick glucose tests alone. In addition to small improvements in A1c and 7% more TIR (without an increase in hypoglycemia), pregnant CGM users had reductions in large-for-gestational age (LGA) births (53% vs 69%, P = .0489), neonatal intensive care admissions lasting more than 24 hours, and severe neonatal hypoglycemia.
Numbers needed to treat to prevent adverse outcomes in the CONCEPTT trial were six for LGA, six for NICU admission, and eight for neonatal hypoglycemia.
Data from the CONCEPTT trial featured prominently in the development of consensus recommendations for CGM targets in pregnancy by an international expert panel endorsed by the American Diabetes Association. In its 2019 report, the group recommended a target range of 63-140 mg/dL for type 1 and type 2 diabetes during pregnancy (compared with 70-180 mg/dL outside of pregnancy), and a TIR > 70% for pregnant people with type 1 diabetes. (Targets for time below range and time above range are also defined for type 1.)
More data are needed, the group said, in order to recommend TIR targets for type 2 diabetes in pregnancy or GDM (Diabetes Care. 2019;42:1593-603). “Many argue,” Dr. Durnwald said, “that there could be more stringent targets for those at less risk for [maternal] hypoglycemia, especially our GDM population.”
There’s a question of whether even higher TIR would further improve perinatal outcomes, she said, “or will we reach a threshold where higher TIR doesn’t get us a [further] reduction in LGA or preeclampsia.”
And while TIR is “certainly our buzzword,” lower mean glucose levels have also been associated with a lower risk of LGA and other adverse neonatal outcomes. A 2019 retrospective study from Sweden, for instance, analyzed patterns of CGM data from 186 pregnant women with type 1 diabetes and found significant associations between elevated mean glucose levels (in the second and third trimesters) and both LGA and an adverse neonatal composite outcome (Diabetologia. 2019;62:1143-53).
Elevated TIR was also associated with LGA, but “mean glucose had the strongest association with the rate of LGA,” Dr. Durnwald said.
Similarly, a 2020 subanalysis of the CONCEPTT trial data found that a higher mean glucose at both 24 and 34 weeks of gestation was significantly associated with a greater risk of LGA (Diabetes Care. 2020;43:1178-84), and a smaller 2015 analysis of data from two randomized controlled trials of CGM in pregnant women with type 1 and type 2 diabetes found this association in trimesters 2 and 3 (Diabetes Care. 2015;38;1319-25).
The ADA’s Standards of Care in Diabetes (Diabetes Care. 2024;47:S282-S294) endorse CGM as an adjunctive tool in pregnancy — not as a replacement for all traditional blood glucose monitoring — and advise that the use of CGM-reported mean glucose is superior to the use of estimated A1c, glucose management indicator, and other calculations to estimate A1c. Changes occur in pregnancy, Dr. Durnwald pointed out. “Most experts will identify a [target] mean glucose < 120 mg/dL in those with type 1, but there’s potential to have a mean glucose closer to 100 in certainly our patients with GDM and some of our patients with type 2,” she said. To a lesser extent, researchers have also looked at the effect of CMG-reported glycemic variability on outcomes such as LGA, with at least two studies finding some association, and there has been some research on nocturnal glucose and LGA, Dr. Durnwald said. CGM “gives us the opportunity,” she said, “to think about nocturnal glucose as a possible target” for further optimizing diabetes management during pregnancy.
CGM in Type 2, GDM
CGM in type 2 diabetes in pregnancy was addressed in a recently published systematic review and meta-analysis, which found only three qualifying randomized controlled trials and concluded that CGM use was not associated with improvements in perinatal outcomes, as assessed by LGA and preeclampsia (Am J Obstet Gynecol MFM. 2023;5:100969). “It’s very limited by the small sample size and the fact that most [patients] were using intermittent CGM,” Dr. Durnwald said. “It highlights how important it is to perform larger studies with continuous CGM.”
While the 2024 ADA standards say there are insufficient data to support the use of CGM in all patients with type 2 diabetes or GDM — and that the decision should be individualized “based on treatment regimen, circumstance, preferences, and needs” — real-world access to CGM for type 2, and even a bit for GDM, is improving, she said.
Some insurers require patients to be on insulin, but the trends are such that “we certainly talk about CGM to all our patients with type 2 diabetes and even our patients with GDM,” Dr. Durnwald said in a later interview. “CGMs are being advertised so we definitely have people who ask about them upon diagnosis, and we try to make it work for them.”
Is Preventing Maternal Hypoglycemia Possible?
Advancements in technology and pharmacology aimed at optimizing glycemic control — increased adoption of CGM, the use of insulin pump therapy, and the use of more rapid insulin analogs — appear to have had little to no impact on rates of severe maternal hypoglycemia in type 1 diabetes in pregnancy, said Dr. Rosenn, referring to several published studies.
The CONCEPTT study in type 1 diabetes, for instance, “gave us the best data we have on the use of CGM,” but differences in the percentage of patients with severe hypoglycemia and the total number of severe hypoglycemia episodes were basically the same whether patients used CGM or not, he said.
Closed-loop insulin delivery systems have been found in nonpregnant patients with type 1 diabetes to “be helpful in keeping people in range and also possibly [decreasing nocturnal hypoglycemia],” but the systems are not approved for use in pregnancy. “There’s not enough data on use in pregnancy, but probably more important, the algorithms used in the closed-loop systems are not directed to the targets we consider ideal for pregnancy,” Dr. Rosenn said.
In a pilot study of a closed-loop delivery system customized for pregnancies complicated by type 1 diabetes, 10 pregnant women were recruited at 14-32 weeks and, after a 1- to 2-week run-in period using a regular CGM-augmented pump, they used the closed-loop system targeting a daytime glucose of 80-110 mg/dL and nocturnal glucose of 80-100 mg/dL.
Mean TIR (a target range of 63-140 mg/dL) increased from 65% during the run-in period to 79% on the closed-loop system, and there were significant decreases in both time above range and time in the hypoglycemic ranges of < 63 mg/dL and < 54 mg/dL. Hypoglycemic events per week (defined as < 54 mg/dL for over 15 minutes) decreased from 4 to 0.7 (Diabetes Care. 2023;46:1425-31).
The investigators are continuing their research, and there are currently two randomized controlled trials underway examining use of closed-loop systems designed for pregnancy, said Dr. Rosenn, who was involved in feasibility research leading up to the pilot study. “So I’m hopeful we’ll see some encouraging information in the future.”
Maternal hypoglycemia during pregnancy is more common in type 1 diabetes, but it also affects pregnancies complicated by type 2 diabetes and GDM. In addition to the strict glycemic control imposed to improve maternal and fetal outcomes, pregnancy itself plays a role.
Research several decades ago from the Diabetes in Pregnancy Program Project, a prospective cohort in Cincinnati which Dr. Rosenn co-led, documented impaired counterregulatory physiology in pregnancy. Even in nondiabetic patients, there are declines in secretion of glucagon and growth hormone in response to hypoglycemia, for instance. In patients with type 1 diabetes, the diminishment in counterregulatory response is more severe.
Rethinking Intrapartum Care
Guidance for tight blood glucose control during labor and delivery for insulin-treated individuals — as reflected in the American College of Obstetricians and Gynecologists Practice Bulletin No. 201 on Pregestational Diabetes and in recommendations from the United Kingdom’s National Institute for Health and Care Excellence (NICE) — is based on small case series and overall “poor-quality” evidence that more recent research has failed to back up, Dr. Bartal said.
A systematic review published in 2018, for example, concluded there is a paucity of high-quality data supporting the association of glucose during labor and delivery with neonatal hypoglycemia in pregnancies complicated by diabetes (Diabet Med. 2018;35:173-83). And in a subsequent retrospective cohort study of pregnant women with type 1/type 2/GDM and their neonates, the same investigators reported no difference in the target glucose in labor between those with and without neonatal hypotension, after adjustment for important neonatal factors such as LGA and preterm delivery (Diabet Med. 2020;37:138-46).
Also exemplifying the body of research, Dr. Bartal said, is another single-center retrospective study published in 2020 that evaluated outcomes in the years before and after the institution of a formal intrapartum insulin regimen (a standardized protocol for titration of insulin and glucose infusions) for women with pregestational or gestational diabetes. The protocol was associated with improved maternal glucose control, but an increased frequency of neonatal hypoglycemia (Obstet Gynecol. 2020;136:411-6).
Her own group at the University of Texas in Houston looked retrospectively at 233 insulin-treated pregnancies complicated by type 2 diabetes and found no significant difference in the rate of neonatal hypoglycemia between those placed on a drip and those who were not, Dr. Bartal said. Over 40% of the newborns had hypoglycemia; it occurred irrespective of the route of delivery as well (J Matern Fetal Neonatal Med. 2022;35:7445-51).
Only two published randomized controlled trials have evaluated blood sugar control in labor, she said. The first, published in 2006, compared a continuous insulin drip with a rotation of glucose and non–glucose-containing fluids in insulin-requiring diabetes and found no differences in maternal blood glucose (the primary outcome) and a similar risk of neonatal hypoglycemia (Am J Obstet Gynecol. 2006;195;1095-9).
The second RCT, published in 2019, evaluated tight versus liberalized control (60-100 mg/dL, checking every hour, versus 60-120 mg/dL, checking every 4 hours) in laboring women with GDM. The first neonatal blood glucose level was similar in both groups, while the mean neonatal blood glucose level in the first 24 hours of life was lower with tight control (54 vs 58 mg/dL, P = .49) (Obstet Gynecol. 2019;133:1171-7). Findings from a new RCT conducted at the University of Texas in Houston of usual care versus more permissive glucose control will be presented at the SMFM Pregnancy Meeting in February 2024, she said.
Neonatal hypoglycemia is associated with increased risk of NICU admission, “but it’s also associated with possible long-term developmental deficit,” Dr. Bartal said, with the risk highest in children exposed to severe, recurrent, or clinically undetected hypoglycemia. Research has documented significantly increased risks of low executive function and visual motor function, for instance, in children who experienced neonatal hypoglycemia.
The risk of neonatal hypoglycemia has been linked to a variety of factors outside of the intrapartum period such as diabetes control and weight gain during pregnancy, neonatal birth weight/LGA, neonatal adiposity, gestational age at delivery, maternal body mass index, smoking, and diabetes control prior to pregnancy, Dr. Bartal noted. Also challenging is the reality that neonatal hypoglycemia as a research outcome is not standardized; definitions have varied across studies.
Tight intrapartum control comes with “costs,” from close monitoring of labor to increased resource utilization, and it may affect the labor experience/satisfaction, Dr. Bartal said. “But furthermore,” she said, “there are studies coming out, especially in the anesthesiology journals, that show there may be possible harm,” such as the risk of maternal and neonatal hyponatremia, and maternal hypoglycemia. A 2016 editorial in Anaesthesia (2016;71:750) describes these concerns, she noted.
“I do think we need to rethink our current recommendations,” she said.
Dr. Durnwald reported serving on the Dexcom GDM advisory board and receiving funding from United Health Group and the Helmsley Charitable Trust. Dr. Bartal and Dr. Rosenn reported no conflicts of interest.
WASHINGTON — Continuous glucose monitoring (CGM) is widely used during pregnancy for individuals with type 1 diabetes — with pregnancy-specific target metrics now chosen and benefits on perinatal outcomes demonstrated — but more research is needed to elucidate its role in the growing population of pregnant people with type 2 diabetes and gestational diabetes (GDM). And overall, there are still “many more questions unanswered about CGM use in pregnancy than what we have answered,” Celeste Durnwald, MD, said at the biennial meeting of the Diabetes in Pregnancy Study Group of North America.
There’s much to learn about how to best interpret “the detailed and complex data that CGM provides,” and what targets in addition to time in range (TIR) are most important, said Dr. Durnwald, director of the perinatal diabetes program and associate professor of ob.gyn. at the Hospital of the University of Pennsylvania, Philadelphia, in a presentation on CGM.
Among other questions are whether fasting glucose is “as important in the era of CGM,” and whether there should be different glycemic targets for nocturnal versus daytime TIR, she said. Moreover, questions justifiably remain about whether the TIR targets for type 1 diabetes in pregnancy are indeed optimal, she said in a discussion period.
Ongoing research is looking at whether CGM can motivate and guide patients with GDM through diet and lifestyle changes such that “we can see changes in amounts of medication we use,” Dr. Durnwald noted in her presentation. “There’s a whole breadth of research looking at whether CGM can help predict diagnosis of GDM, large for gestational age, or preeclampsia, and what are the targets.”
Maternal hypoglycemia during pregnancy — a time when strict glycemic control is recommended to reduce the risk of congenital malformations and other fetal and neonatal morbidity — remains a concern in type 1 diabetes, even with widespread use of CGM in this population, said Barak Rosenn, MD, during a presentation on glycemic control in type 1 diabetes.
A pilot study of a newly designed pregnancy-specific closed-loop insulin delivery system, published last year (Diabetes Care. 2023;46:1425-31), has offered the first “really encouraging information about the ability to use our most up-to-date technology to help our type 1 patients maintain strict control and at the same time decrease their risk of severe hypoglycemia,” said Dr. Rosenn, a maternal-fetal medicine specialist at the Jersey City Medical Center, Jersey City, New Jersey.
Guidance for tight intrapartum glucose control, meanwhile, has been backed by little evidence, said Michal Fishel Bartal, MD, MS, and some recent studies and reviews have shown little to no effect of such tight control on neonatal hypoglycemia, which is the aim of the guidance.
“We need to reexamine current recommendations,” said Dr. Bartal, assistant professor in the division of maternal-fetal medicine at the University of Texas Health Science Center, Houston, during a presentation on intrapartum care. “There’s very limited evidence-based data for the way we manage people with diabetes [during labor and delivery].”
The Knowns And Unknowns of CGM in Pregnancy
The multicenter, international CONCEPTT trial (Continuous Glucose Monitoring in Pregnant Women With Type 1 Diabetes), published in 2017, was the first trial to demonstrate improvements in perinatal outcomes, and it “brought CGM to the forefront in terms of widespread use,” Dr. Durnwald said.
The trial randomized more than 300 patients with type 1 diabetes who were pregnant or planning pregnancy (both users of insulin pumps and users of multiple insulin injections) to continuous, real-time CGM in addition to finger-stick glucose monitoring, or standard finger-stick glucose tests alone. In addition to small improvements in A1c and 7% more TIR (without an increase in hypoglycemia), pregnant CGM users had reductions in large-for-gestational age (LGA) births (53% vs 69%, P = .0489), neonatal intensive care admissions lasting more than 24 hours, and severe neonatal hypoglycemia.
Numbers needed to treat to prevent adverse outcomes in the CONCEPTT trial were six for LGA, six for NICU admission, and eight for neonatal hypoglycemia.
Data from the CONCEPTT trial featured prominently in the development of consensus recommendations for CGM targets in pregnancy by an international expert panel endorsed by the American Diabetes Association. In its 2019 report, the group recommended a target range of 63-140 mg/dL for type 1 and type 2 diabetes during pregnancy (compared with 70-180 mg/dL outside of pregnancy), and a TIR > 70% for pregnant people with type 1 diabetes. (Targets for time below range and time above range are also defined for type 1.)
More data are needed, the group said, in order to recommend TIR targets for type 2 diabetes in pregnancy or GDM (Diabetes Care. 2019;42:1593-603). “Many argue,” Dr. Durnwald said, “that there could be more stringent targets for those at less risk for [maternal] hypoglycemia, especially our GDM population.”
There’s a question of whether even higher TIR would further improve perinatal outcomes, she said, “or will we reach a threshold where higher TIR doesn’t get us a [further] reduction in LGA or preeclampsia.”
And while TIR is “certainly our buzzword,” lower mean glucose levels have also been associated with a lower risk of LGA and other adverse neonatal outcomes. A 2019 retrospective study from Sweden, for instance, analyzed patterns of CGM data from 186 pregnant women with type 1 diabetes and found significant associations between elevated mean glucose levels (in the second and third trimesters) and both LGA and an adverse neonatal composite outcome (Diabetologia. 2019;62:1143-53).
Elevated TIR was also associated with LGA, but “mean glucose had the strongest association with the rate of LGA,” Dr. Durnwald said.
Similarly, a 2020 subanalysis of the CONCEPTT trial data found that a higher mean glucose at both 24 and 34 weeks of gestation was significantly associated with a greater risk of LGA (Diabetes Care. 2020;43:1178-84), and a smaller 2015 analysis of data from two randomized controlled trials of CGM in pregnant women with type 1 and type 2 diabetes found this association in trimesters 2 and 3 (Diabetes Care. 2015;38;1319-25).
The ADA’s Standards of Care in Diabetes (Diabetes Care. 2024;47:S282-S294) endorse CGM as an adjunctive tool in pregnancy — not as a replacement for all traditional blood glucose monitoring — and advise that the use of CGM-reported mean glucose is superior to the use of estimated A1c, glucose management indicator, and other calculations to estimate A1c. Changes occur in pregnancy, Dr. Durnwald pointed out. “Most experts will identify a [target] mean glucose < 120 mg/dL in those with type 1, but there’s potential to have a mean glucose closer to 100 in certainly our patients with GDM and some of our patients with type 2,” she said. To a lesser extent, researchers have also looked at the effect of CMG-reported glycemic variability on outcomes such as LGA, with at least two studies finding some association, and there has been some research on nocturnal glucose and LGA, Dr. Durnwald said. CGM “gives us the opportunity,” she said, “to think about nocturnal glucose as a possible target” for further optimizing diabetes management during pregnancy.
CGM in Type 2, GDM
CGM in type 2 diabetes in pregnancy was addressed in a recently published systematic review and meta-analysis, which found only three qualifying randomized controlled trials and concluded that CGM use was not associated with improvements in perinatal outcomes, as assessed by LGA and preeclampsia (Am J Obstet Gynecol MFM. 2023;5:100969). “It’s very limited by the small sample size and the fact that most [patients] were using intermittent CGM,” Dr. Durnwald said. “It highlights how important it is to perform larger studies with continuous CGM.”
While the 2024 ADA standards say there are insufficient data to support the use of CGM in all patients with type 2 diabetes or GDM — and that the decision should be individualized “based on treatment regimen, circumstance, preferences, and needs” — real-world access to CGM for type 2, and even a bit for GDM, is improving, she said.
Some insurers require patients to be on insulin, but the trends are such that “we certainly talk about CGM to all our patients with type 2 diabetes and even our patients with GDM,” Dr. Durnwald said in a later interview. “CGMs are being advertised so we definitely have people who ask about them upon diagnosis, and we try to make it work for them.”
Is Preventing Maternal Hypoglycemia Possible?
Advancements in technology and pharmacology aimed at optimizing glycemic control — increased adoption of CGM, the use of insulin pump therapy, and the use of more rapid insulin analogs — appear to have had little to no impact on rates of severe maternal hypoglycemia in type 1 diabetes in pregnancy, said Dr. Rosenn, referring to several published studies.
The CONCEPTT study in type 1 diabetes, for instance, “gave us the best data we have on the use of CGM,” but differences in the percentage of patients with severe hypoglycemia and the total number of severe hypoglycemia episodes were basically the same whether patients used CGM or not, he said.
Closed-loop insulin delivery systems have been found in nonpregnant patients with type 1 diabetes to “be helpful in keeping people in range and also possibly [decreasing nocturnal hypoglycemia],” but the systems are not approved for use in pregnancy. “There’s not enough data on use in pregnancy, but probably more important, the algorithms used in the closed-loop systems are not directed to the targets we consider ideal for pregnancy,” Dr. Rosenn said.
In a pilot study of a closed-loop delivery system customized for pregnancies complicated by type 1 diabetes, 10 pregnant women were recruited at 14-32 weeks and, after a 1- to 2-week run-in period using a regular CGM-augmented pump, they used the closed-loop system targeting a daytime glucose of 80-110 mg/dL and nocturnal glucose of 80-100 mg/dL.
Mean TIR (a target range of 63-140 mg/dL) increased from 65% during the run-in period to 79% on the closed-loop system, and there were significant decreases in both time above range and time in the hypoglycemic ranges of < 63 mg/dL and < 54 mg/dL. Hypoglycemic events per week (defined as < 54 mg/dL for over 15 minutes) decreased from 4 to 0.7 (Diabetes Care. 2023;46:1425-31).
The investigators are continuing their research, and there are currently two randomized controlled trials underway examining use of closed-loop systems designed for pregnancy, said Dr. Rosenn, who was involved in feasibility research leading up to the pilot study. “So I’m hopeful we’ll see some encouraging information in the future.”
Maternal hypoglycemia during pregnancy is more common in type 1 diabetes, but it also affects pregnancies complicated by type 2 diabetes and GDM. In addition to the strict glycemic control imposed to improve maternal and fetal outcomes, pregnancy itself plays a role.
Research several decades ago from the Diabetes in Pregnancy Program Project, a prospective cohort in Cincinnati which Dr. Rosenn co-led, documented impaired counterregulatory physiology in pregnancy. Even in nondiabetic patients, there are declines in secretion of glucagon and growth hormone in response to hypoglycemia, for instance. In patients with type 1 diabetes, the diminishment in counterregulatory response is more severe.
Rethinking Intrapartum Care
Guidance for tight blood glucose control during labor and delivery for insulin-treated individuals — as reflected in the American College of Obstetricians and Gynecologists Practice Bulletin No. 201 on Pregestational Diabetes and in recommendations from the United Kingdom’s National Institute for Health and Care Excellence (NICE) — is based on small case series and overall “poor-quality” evidence that more recent research has failed to back up, Dr. Bartal said.
A systematic review published in 2018, for example, concluded there is a paucity of high-quality data supporting the association of glucose during labor and delivery with neonatal hypoglycemia in pregnancies complicated by diabetes (Diabet Med. 2018;35:173-83). And in a subsequent retrospective cohort study of pregnant women with type 1/type 2/GDM and their neonates, the same investigators reported no difference in the target glucose in labor between those with and without neonatal hypotension, after adjustment for important neonatal factors such as LGA and preterm delivery (Diabet Med. 2020;37:138-46).
Also exemplifying the body of research, Dr. Bartal said, is another single-center retrospective study published in 2020 that evaluated outcomes in the years before and after the institution of a formal intrapartum insulin regimen (a standardized protocol for titration of insulin and glucose infusions) for women with pregestational or gestational diabetes. The protocol was associated with improved maternal glucose control, but an increased frequency of neonatal hypoglycemia (Obstet Gynecol. 2020;136:411-6).
Her own group at the University of Texas in Houston looked retrospectively at 233 insulin-treated pregnancies complicated by type 2 diabetes and found no significant difference in the rate of neonatal hypoglycemia between those placed on a drip and those who were not, Dr. Bartal said. Over 40% of the newborns had hypoglycemia; it occurred irrespective of the route of delivery as well (J Matern Fetal Neonatal Med. 2022;35:7445-51).
Only two published randomized controlled trials have evaluated blood sugar control in labor, she said. The first, published in 2006, compared a continuous insulin drip with a rotation of glucose and non–glucose-containing fluids in insulin-requiring diabetes and found no differences in maternal blood glucose (the primary outcome) and a similar risk of neonatal hypoglycemia (Am J Obstet Gynecol. 2006;195;1095-9).
The second RCT, published in 2019, evaluated tight versus liberalized control (60-100 mg/dL, checking every hour, versus 60-120 mg/dL, checking every 4 hours) in laboring women with GDM. The first neonatal blood glucose level was similar in both groups, while the mean neonatal blood glucose level in the first 24 hours of life was lower with tight control (54 vs 58 mg/dL, P = .49) (Obstet Gynecol. 2019;133:1171-7). Findings from a new RCT conducted at the University of Texas in Houston of usual care versus more permissive glucose control will be presented at the SMFM Pregnancy Meeting in February 2024, she said.
Neonatal hypoglycemia is associated with increased risk of NICU admission, “but it’s also associated with possible long-term developmental deficit,” Dr. Bartal said, with the risk highest in children exposed to severe, recurrent, or clinically undetected hypoglycemia. Research has documented significantly increased risks of low executive function and visual motor function, for instance, in children who experienced neonatal hypoglycemia.
The risk of neonatal hypoglycemia has been linked to a variety of factors outside of the intrapartum period such as diabetes control and weight gain during pregnancy, neonatal birth weight/LGA, neonatal adiposity, gestational age at delivery, maternal body mass index, smoking, and diabetes control prior to pregnancy, Dr. Bartal noted. Also challenging is the reality that neonatal hypoglycemia as a research outcome is not standardized; definitions have varied across studies.
Tight intrapartum control comes with “costs,” from close monitoring of labor to increased resource utilization, and it may affect the labor experience/satisfaction, Dr. Bartal said. “But furthermore,” she said, “there are studies coming out, especially in the anesthesiology journals, that show there may be possible harm,” such as the risk of maternal and neonatal hyponatremia, and maternal hypoglycemia. A 2016 editorial in Anaesthesia (2016;71:750) describes these concerns, she noted.
“I do think we need to rethink our current recommendations,” she said.
Dr. Durnwald reported serving on the Dexcom GDM advisory board and receiving funding from United Health Group and the Helmsley Charitable Trust. Dr. Bartal and Dr. Rosenn reported no conflicts of interest.
WASHINGTON — Continuous glucose monitoring (CGM) is widely used during pregnancy for individuals with type 1 diabetes — with pregnancy-specific target metrics now chosen and benefits on perinatal outcomes demonstrated — but more research is needed to elucidate its role in the growing population of pregnant people with type 2 diabetes and gestational diabetes (GDM). And overall, there are still “many more questions unanswered about CGM use in pregnancy than what we have answered,” Celeste Durnwald, MD, said at the biennial meeting of the Diabetes in Pregnancy Study Group of North America.
There’s much to learn about how to best interpret “the detailed and complex data that CGM provides,” and what targets in addition to time in range (TIR) are most important, said Dr. Durnwald, director of the perinatal diabetes program and associate professor of ob.gyn. at the Hospital of the University of Pennsylvania, Philadelphia, in a presentation on CGM.
Among other questions are whether fasting glucose is “as important in the era of CGM,” and whether there should be different glycemic targets for nocturnal versus daytime TIR, she said. Moreover, questions justifiably remain about whether the TIR targets for type 1 diabetes in pregnancy are indeed optimal, she said in a discussion period.
Ongoing research is looking at whether CGM can motivate and guide patients with GDM through diet and lifestyle changes such that “we can see changes in amounts of medication we use,” Dr. Durnwald noted in her presentation. “There’s a whole breadth of research looking at whether CGM can help predict diagnosis of GDM, large for gestational age, or preeclampsia, and what are the targets.”
Maternal hypoglycemia during pregnancy — a time when strict glycemic control is recommended to reduce the risk of congenital malformations and other fetal and neonatal morbidity — remains a concern in type 1 diabetes, even with widespread use of CGM in this population, said Barak Rosenn, MD, during a presentation on glycemic control in type 1 diabetes.
A pilot study of a newly designed pregnancy-specific closed-loop insulin delivery system, published last year (Diabetes Care. 2023;46:1425-31), has offered the first “really encouraging information about the ability to use our most up-to-date technology to help our type 1 patients maintain strict control and at the same time decrease their risk of severe hypoglycemia,” said Dr. Rosenn, a maternal-fetal medicine specialist at the Jersey City Medical Center, Jersey City, New Jersey.
Guidance for tight intrapartum glucose control, meanwhile, has been backed by little evidence, said Michal Fishel Bartal, MD, MS, and some recent studies and reviews have shown little to no effect of such tight control on neonatal hypoglycemia, which is the aim of the guidance.
“We need to reexamine current recommendations,” said Dr. Bartal, assistant professor in the division of maternal-fetal medicine at the University of Texas Health Science Center, Houston, during a presentation on intrapartum care. “There’s very limited evidence-based data for the way we manage people with diabetes [during labor and delivery].”
The Knowns And Unknowns of CGM in Pregnancy
The multicenter, international CONCEPTT trial (Continuous Glucose Monitoring in Pregnant Women With Type 1 Diabetes), published in 2017, was the first trial to demonstrate improvements in perinatal outcomes, and it “brought CGM to the forefront in terms of widespread use,” Dr. Durnwald said.
The trial randomized more than 300 patients with type 1 diabetes who were pregnant or planning pregnancy (both users of insulin pumps and users of multiple insulin injections) to continuous, real-time CGM in addition to finger-stick glucose monitoring, or standard finger-stick glucose tests alone. In addition to small improvements in A1c and 7% more TIR (without an increase in hypoglycemia), pregnant CGM users had reductions in large-for-gestational age (LGA) births (53% vs 69%, P = .0489), neonatal intensive care admissions lasting more than 24 hours, and severe neonatal hypoglycemia.
Numbers needed to treat to prevent adverse outcomes in the CONCEPTT trial were six for LGA, six for NICU admission, and eight for neonatal hypoglycemia.
Data from the CONCEPTT trial featured prominently in the development of consensus recommendations for CGM targets in pregnancy by an international expert panel endorsed by the American Diabetes Association. In its 2019 report, the group recommended a target range of 63-140 mg/dL for type 1 and type 2 diabetes during pregnancy (compared with 70-180 mg/dL outside of pregnancy), and a TIR > 70% for pregnant people with type 1 diabetes. (Targets for time below range and time above range are also defined for type 1.)
More data are needed, the group said, in order to recommend TIR targets for type 2 diabetes in pregnancy or GDM (Diabetes Care. 2019;42:1593-603). “Many argue,” Dr. Durnwald said, “that there could be more stringent targets for those at less risk for [maternal] hypoglycemia, especially our GDM population.”
There’s a question of whether even higher TIR would further improve perinatal outcomes, she said, “or will we reach a threshold where higher TIR doesn’t get us a [further] reduction in LGA or preeclampsia.”
And while TIR is “certainly our buzzword,” lower mean glucose levels have also been associated with a lower risk of LGA and other adverse neonatal outcomes. A 2019 retrospective study from Sweden, for instance, analyzed patterns of CGM data from 186 pregnant women with type 1 diabetes and found significant associations between elevated mean glucose levels (in the second and third trimesters) and both LGA and an adverse neonatal composite outcome (Diabetologia. 2019;62:1143-53).
Elevated TIR was also associated with LGA, but “mean glucose had the strongest association with the rate of LGA,” Dr. Durnwald said.
Similarly, a 2020 subanalysis of the CONCEPTT trial data found that a higher mean glucose at both 24 and 34 weeks of gestation was significantly associated with a greater risk of LGA (Diabetes Care. 2020;43:1178-84), and a smaller 2015 analysis of data from two randomized controlled trials of CGM in pregnant women with type 1 and type 2 diabetes found this association in trimesters 2 and 3 (Diabetes Care. 2015;38;1319-25).
The ADA’s Standards of Care in Diabetes (Diabetes Care. 2024;47:S282-S294) endorse CGM as an adjunctive tool in pregnancy — not as a replacement for all traditional blood glucose monitoring — and advise that the use of CGM-reported mean glucose is superior to the use of estimated A1c, glucose management indicator, and other calculations to estimate A1c. Changes occur in pregnancy, Dr. Durnwald pointed out. “Most experts will identify a [target] mean glucose < 120 mg/dL in those with type 1, but there’s potential to have a mean glucose closer to 100 in certainly our patients with GDM and some of our patients with type 2,” she said. To a lesser extent, researchers have also looked at the effect of CMG-reported glycemic variability on outcomes such as LGA, with at least two studies finding some association, and there has been some research on nocturnal glucose and LGA, Dr. Durnwald said. CGM “gives us the opportunity,” she said, “to think about nocturnal glucose as a possible target” for further optimizing diabetes management during pregnancy.
CGM in Type 2, GDM
CGM in type 2 diabetes in pregnancy was addressed in a recently published systematic review and meta-analysis, which found only three qualifying randomized controlled trials and concluded that CGM use was not associated with improvements in perinatal outcomes, as assessed by LGA and preeclampsia (Am J Obstet Gynecol MFM. 2023;5:100969). “It’s very limited by the small sample size and the fact that most [patients] were using intermittent CGM,” Dr. Durnwald said. “It highlights how important it is to perform larger studies with continuous CGM.”
While the 2024 ADA standards say there are insufficient data to support the use of CGM in all patients with type 2 diabetes or GDM — and that the decision should be individualized “based on treatment regimen, circumstance, preferences, and needs” — real-world access to CGM for type 2, and even a bit for GDM, is improving, she said.
Some insurers require patients to be on insulin, but the trends are such that “we certainly talk about CGM to all our patients with type 2 diabetes and even our patients with GDM,” Dr. Durnwald said in a later interview. “CGMs are being advertised so we definitely have people who ask about them upon diagnosis, and we try to make it work for them.”
Is Preventing Maternal Hypoglycemia Possible?
Advancements in technology and pharmacology aimed at optimizing glycemic control — increased adoption of CGM, the use of insulin pump therapy, and the use of more rapid insulin analogs — appear to have had little to no impact on rates of severe maternal hypoglycemia in type 1 diabetes in pregnancy, said Dr. Rosenn, referring to several published studies.
The CONCEPTT study in type 1 diabetes, for instance, “gave us the best data we have on the use of CGM,” but differences in the percentage of patients with severe hypoglycemia and the total number of severe hypoglycemia episodes were basically the same whether patients used CGM or not, he said.
Closed-loop insulin delivery systems have been found in nonpregnant patients with type 1 diabetes to “be helpful in keeping people in range and also possibly [decreasing nocturnal hypoglycemia],” but the systems are not approved for use in pregnancy. “There’s not enough data on use in pregnancy, but probably more important, the algorithms used in the closed-loop systems are not directed to the targets we consider ideal for pregnancy,” Dr. Rosenn said.
In a pilot study of a closed-loop delivery system customized for pregnancies complicated by type 1 diabetes, 10 pregnant women were recruited at 14-32 weeks and, after a 1- to 2-week run-in period using a regular CGM-augmented pump, they used the closed-loop system targeting a daytime glucose of 80-110 mg/dL and nocturnal glucose of 80-100 mg/dL.
Mean TIR (a target range of 63-140 mg/dL) increased from 65% during the run-in period to 79% on the closed-loop system, and there were significant decreases in both time above range and time in the hypoglycemic ranges of < 63 mg/dL and < 54 mg/dL. Hypoglycemic events per week (defined as < 54 mg/dL for over 15 minutes) decreased from 4 to 0.7 (Diabetes Care. 2023;46:1425-31).
The investigators are continuing their research, and there are currently two randomized controlled trials underway examining use of closed-loop systems designed for pregnancy, said Dr. Rosenn, who was involved in feasibility research leading up to the pilot study. “So I’m hopeful we’ll see some encouraging information in the future.”
Maternal hypoglycemia during pregnancy is more common in type 1 diabetes, but it also affects pregnancies complicated by type 2 diabetes and GDM. In addition to the strict glycemic control imposed to improve maternal and fetal outcomes, pregnancy itself plays a role.
Research several decades ago from the Diabetes in Pregnancy Program Project, a prospective cohort in Cincinnati which Dr. Rosenn co-led, documented impaired counterregulatory physiology in pregnancy. Even in nondiabetic patients, there are declines in secretion of glucagon and growth hormone in response to hypoglycemia, for instance. In patients with type 1 diabetes, the diminishment in counterregulatory response is more severe.
Rethinking Intrapartum Care
Guidance for tight blood glucose control during labor and delivery for insulin-treated individuals — as reflected in the American College of Obstetricians and Gynecologists Practice Bulletin No. 201 on Pregestational Diabetes and in recommendations from the United Kingdom’s National Institute for Health and Care Excellence (NICE) — is based on small case series and overall “poor-quality” evidence that more recent research has failed to back up, Dr. Bartal said.
A systematic review published in 2018, for example, concluded there is a paucity of high-quality data supporting the association of glucose during labor and delivery with neonatal hypoglycemia in pregnancies complicated by diabetes (Diabet Med. 2018;35:173-83). And in a subsequent retrospective cohort study of pregnant women with type 1/type 2/GDM and their neonates, the same investigators reported no difference in the target glucose in labor between those with and without neonatal hypotension, after adjustment for important neonatal factors such as LGA and preterm delivery (Diabet Med. 2020;37:138-46).
Also exemplifying the body of research, Dr. Bartal said, is another single-center retrospective study published in 2020 that evaluated outcomes in the years before and after the institution of a formal intrapartum insulin regimen (a standardized protocol for titration of insulin and glucose infusions) for women with pregestational or gestational diabetes. The protocol was associated with improved maternal glucose control, but an increased frequency of neonatal hypoglycemia (Obstet Gynecol. 2020;136:411-6).
Her own group at the University of Texas in Houston looked retrospectively at 233 insulin-treated pregnancies complicated by type 2 diabetes and found no significant difference in the rate of neonatal hypoglycemia between those placed on a drip and those who were not, Dr. Bartal said. Over 40% of the newborns had hypoglycemia; it occurred irrespective of the route of delivery as well (J Matern Fetal Neonatal Med. 2022;35:7445-51).
Only two published randomized controlled trials have evaluated blood sugar control in labor, she said. The first, published in 2006, compared a continuous insulin drip with a rotation of glucose and non–glucose-containing fluids in insulin-requiring diabetes and found no differences in maternal blood glucose (the primary outcome) and a similar risk of neonatal hypoglycemia (Am J Obstet Gynecol. 2006;195;1095-9).
The second RCT, published in 2019, evaluated tight versus liberalized control (60-100 mg/dL, checking every hour, versus 60-120 mg/dL, checking every 4 hours) in laboring women with GDM. The first neonatal blood glucose level was similar in both groups, while the mean neonatal blood glucose level in the first 24 hours of life was lower with tight control (54 vs 58 mg/dL, P = .49) (Obstet Gynecol. 2019;133:1171-7). Findings from a new RCT conducted at the University of Texas in Houston of usual care versus more permissive glucose control will be presented at the SMFM Pregnancy Meeting in February 2024, she said.
Neonatal hypoglycemia is associated with increased risk of NICU admission, “but it’s also associated with possible long-term developmental deficit,” Dr. Bartal said, with the risk highest in children exposed to severe, recurrent, or clinically undetected hypoglycemia. Research has documented significantly increased risks of low executive function and visual motor function, for instance, in children who experienced neonatal hypoglycemia.
The risk of neonatal hypoglycemia has been linked to a variety of factors outside of the intrapartum period such as diabetes control and weight gain during pregnancy, neonatal birth weight/LGA, neonatal adiposity, gestational age at delivery, maternal body mass index, smoking, and diabetes control prior to pregnancy, Dr. Bartal noted. Also challenging is the reality that neonatal hypoglycemia as a research outcome is not standardized; definitions have varied across studies.
Tight intrapartum control comes with “costs,” from close monitoring of labor to increased resource utilization, and it may affect the labor experience/satisfaction, Dr. Bartal said. “But furthermore,” she said, “there are studies coming out, especially in the anesthesiology journals, that show there may be possible harm,” such as the risk of maternal and neonatal hyponatremia, and maternal hypoglycemia. A 2016 editorial in Anaesthesia (2016;71:750) describes these concerns, she noted.
“I do think we need to rethink our current recommendations,” she said.
Dr. Durnwald reported serving on the Dexcom GDM advisory board and receiving funding from United Health Group and the Helmsley Charitable Trust. Dr. Bartal and Dr. Rosenn reported no conflicts of interest.
FROM DPSG-NA 2024