Can gestational diabetes be prevented?
Diet and exercise interventions have been suggested to reduce the risk for gestational diabetes, but the results have been inconclusive. A review of 13 moderate-quality randomized controlled trials found no clear difference in the risk for developing gestational diabetes in women receiving a combined diet and exercise intervention vs those receiving no intervention.3 In contrast, a review of 15 randomized controlled trials found combined lifestyle programs to have better efficacy in reducing gestational diabetes prevalence than single interventions targeting only diet or exercise.4
Supplements to prevent gestational diabetes have been studied, with myo-inositol and probiotics showing promise.4 A myo-inositol study reported a reduction in the rate of gestational diabetes from 28% to between 8% and 18%,5 whereas a probiotic study reported a 60% decrease in gestational diabetes in women taking probiotics from early pregnancy.6 Both studies had low-quality evidence.
Which factors increase the risk of gestational diabetes?
Numerous factors are known to increase the risk of gestational diabetes, including age older than 25 years; being overweight or obese before pregnancy; a history of glucose intolerance, diabetes, or a complicated previous delivery (eg, baby weighed greater than 9 lb, stillbirth); a history of diabetes in a first-degree relative; and being nonwhite.7 When examining race, Asian Indian, Native Hawaiian, Pacific Islander, Hispanic, and black women have been found to have a higher risk for developing gestational diabetes than non-Hispanic white women, with risk highest among women born outside of the United States.8
Studies continue to identify potential risk factors for gestational diabetes, with recently published studies reporting an increased risk among women conceiving during the winter months9 and among those with elevated iron stores during early to mid-pregnancy.10 Although confirmatory studies are needed, such studies highlight the complex pathogenesis of gestational diabetes.
How is gestational diabetes diagnosed?
The ADA recommends risk assessment for gestational diabetes at the first prenatal visit.1 High-risk women should receive glucose testing as soon as possible. If no gestational diabetes is found, they should be retested at 24 to 28 weeks of gestation. Low- and average-risk asymptomatic women should receive gestational diabetes testing between 24 and 28 weeks of gestation.1
Gestational diabetes can be screened for using a 1- or 2-step approach.1 The 1-step approach uses an oral glucose tolerance test (OGTT). After fasting glucose levels are tested, patients receive a 75-g glucose load and have their plasma glucose levels assessed 1 and 2 hours later. The 2-step approach involves performing a 50-g oral glucose challenge test in a nonfasting state. If the screening threshold is met or exceeded, the patient receives an OGTT. The same procedure is followed as in the 1-step approach, except a 100-g glucose load is used and glucose levels are also assessed at the 3-hour mark. Gestational diabetes is diagnosed when at least 2 glucose values fall at or above glucose thresholds (usually greater than 130 mg/dL).1
What maternal risks are associated with gestational diabetes?
Gestational diabetes is associated with numerous maternal risks, including a higher risk for hypertensive disorders during pregnancy, including life-threatening preeclampsia, and future risk for metabolic syndrome, including obesity, cardiovascular morbidities, and recurrent gestational diabetes, increasing the risk for subsequent type 2 diabetes. One study found the risk for hypertensive disorders to reach 17% in the gestational diabetes population vs 12% in women without diabetes.11 The cumulative incidence of subsequent type 2 diabetes has been reported to range from 2.6% to greater than 70% in studies examining women 6 weeks postpartum to 28 years postpartum, with risk being highest in the first 5 years following delivery and plateauing after 10 years.12
Patients with gestational diabetes are also at higher risk for Cesarean delivery, with 1 study reporting an incidence of 30% in these patients (vs 17% in those without).11 Additionally, because their fetuses tend to be larger, women with gestational diabetes are at higher risk for postpartum hemorrhage, birth trauma, and shoulder dystocia.11
What fetal risks are associated with gestational diabetes?
Untreated moderate or severe diabetes during pregnancy increases the risk for fetal and neonatal complications, including preterm delivery, macrosomia, and hypoglycemia.7 It is also associated with an increased risk for congenital malformations, such as orofacial clefts, cardiovascular defects, esophageal/intestinal atresia, hypospadias, and spinal malformations.13 Furthermore, fasting hyperglycemia increases the risk for intrauterine fetal death, with 1 study finding women with gestational diabetes to have a more than 4 times greater risk for fetal death than their counterparts without diabetes.14
The increased risk for death persists through infancy, with a reported rate nearly double that of infants born to mothers without diabetes.14 The risks posed by gestational diabetes continue after infanthood. Babies of mothers who had gestational diabetes or type 2 diabetes during pregnancy are at higher risk for developing obesity and type 2 diabetes later in life.7
How is gestational diabetes managed?
Lifestyle change is an essential component of managing gestational diabetes, with population studies indicating 70% to 85% of gestational diabetes cases can be successfully managed this way.1 Lifestyle modifications might include dietary adjustments, increased physical activity, and weight management for overweight patients.
To ensure lifestyle interventions are successfully controlling blood glucose levels, regular home monitoring is essential, with most patients needing to test their blood glucose levels daily. Patients should strive to achieve the following blood glucose targets: fasting ≤95 mg/dL and either 1-hour postprandial ≤140 mg/dL or 2-hour postprandial ≤120 mg/dL. If these targets are not achieved with lifestyle modification, medication should be added to achieve glycemic targets.1
What dietary and exercise interventions are recommended?
Patients with gestational diabetes must pay attention to their carbohydrate intake, taking care to limit consumption of starchy and high-sugar foods and beverages. More recently, researchers have sought to determine whether use of a diet higher in nutrient-dense carbohydrate would be preferable to a traditional low-carbohydrate diet, but the data to recommend this approach remain insufficient.15 Ideally, patients with gestational diabetes would work with a nutritionist to optimize their diet.
Currently, there are no formal guidelines for exercise in gestational diabetes; however, the same precautions should be taken as in other pregnant women, with the additional consideration of hypoglycemia risk, which is affected by frequency, intensity, time/duration, and type of exercise.16 In general, a combination of aerobic and resistance exercise performed at moderate intensity 3 times a week for 30- to 60-minutes each session is considered safe. Consultation with an exercise trainer versed in gestational diabetes can be beneficial.16
What medications can be used if needed to control gestational diabetes?
When medication is needed to obtain blood glucose targets, insulin and metformin are preferred.1 Metformin is preferable to insulin if it provides sufficient glucose control because it is associated with a lower risk for hypoglycemia and weight gain; however, its use might increase the risk for prematurity. When insulin is needed, referral to a specialty center offering team-based care should be considered because of the complexity of insulin dosing in pregnant patients.1
Glyburide may be considered, but more recent studies have associated its use with a higher risk for neonatal hypoglycemia and macrosomia compared with insulin or metformin.1 Other agents have not been adequately studied. Regardless of agent(s) used, patients should be informed that most oral agents cross the placenta, and all lack long-term safety data.1
What kind of postnatal monitoring should be undertaken?
A 75-g OGTT is recommended at the 6- to 12-week postpartum visit.1 This test is preferred to an HbA1c test, which can be inaccurate secondary to increased red blood cell turnover from pregnancy or blood loss at delivery.
Because gestational diabetes increases the risk for subsequent type 2 diabetes, women with a normal postpartum OGTT should continue to be tested every 1 to 3 years thereafter, with frequency of screening depending on other risk factors (eg, family history, prepregnancy body mass index). Ongoing screening may be performed with any glycemic test, including HbA1c, fasting plasma glucose, or 75-g OGTT, and nonpregnant thresholds should be used.1
Historically, gestational diabetes has been defined as impaired glucose tolerance with onset or first recognition during pregnancy.1 However, the increasing prevalence of obesity and diabetes has led to more women of childbearing age having undiagnosed type 2 diabetes, prompting the American Diabetes Association (ADA) to update its definition of gestational diabetes. Currently, only women diagnosed during the second or third trimester should be considered to have gestational diabetes. Those diagnosed during their first trimester should be considered to have type 2 diabetes.1
According to a 2014 Centers for Disease Control and Prevention report, the prevalence of gestational diabetes in the United States may be as high as 9.2%.2 Previous reports have estimated gestational diabetes to occur in 1% to 14% of pregnancies, depending on the diagnostic test used and the population studied, with a trend towards steadily increasing prevalence as the incidence of obesity and diabetes continue to rise.2 Because unrecognized and untreated gestational diabetes can have profound immediate and long-term risks for mother and child, prompt recognition and proper management are essential in reducing the risk for complications and optimizing outcomes.
- American Diabetes Association Standards of Medical Care in Diabetes—2016.Diabetes Care. 2016;39(Suppl 1):S1-S112..
- DeSisto CL, Kim SY, Sharma AJ, et al. Prevalence Estimates of Gestational Diabetes Mellitus in the United States, Pregnancy Risk Assessment Monitoring System (PRAMS), 2007-2010. Prev Chronic Dis. 2014;11:130415.
- Bain E, Crane M, Tieu J, Han S, Crowther CA, Middleton P. Diet and exercise interventions for preventing gestational diabetes mellitus. Cochrane Database Syst Rev. 2015;(4):CD010443. doi:10.1002/14651858.CD010443.pub2.
- Facchinetti F, Dante G, Petrella E, Neri I. Dietary interventions, lifestyle changes, and dietary supplements in preventing gestational diabetes mellitus: a literature review. Obstet Gynecol Surv. 2014;69(11):669-680. doi:10.1097/OGX.0000000000000121.
- Crawford TJ, Crowther CA, Alsweiler J, Brown J. Antenatal dietary supplementation with myo-inositol in women during pregnancy for preventing gestational diabetes. Cochrane Database Syst Rev. 2015 Dec 17. doi:10.1002/14651858.CD011507.pub2.
- Barrett HL, Dekker Nitert M, Conwell LS, Callaway L. Probiotics for preventing gestational diabetes. Cochrane Database Syst Rev. 2014 Feb 27. doi:10.1002/14651858.CD009951.pub2. onlinelibrary.wiley.com/doi/10.1002/14651858.CD009951.pub2/epdf. Published February 27, 2014. Accessed November 20, 2016.
- American Diabetes Association. Gestational diabetes mellitus. Diabetes Care. 2003;26(Suppl 1):S103-S105.
- Fujimoto WF, Samoa R, Wotring A. Gestational diabetes in high-risk populations. Clin Diabetes. 2013;31(2):90-94.
- Verburg PE, Tucker G, Scheil W, et al. Seasonality of gestational diabetes mellitus: a South Australian population study. BMJ Open Diabetes Research and Care. 2016;4:e000286. doi:10.1136/bmjdrc-2016-000286.
- Rawal S, Hinkle SN, Bao W, et al. A longitudinal study of iron status during pregnancy and the risk of gestational diabetes: findings from a prospective, multiracial cohort. Diabetologia. 2016 Nov 10. doi:10.1007/s00125-016-4149-3 [Epub ahead of print].
- Casey BM, Lucas MJ, Mcintire DD, Leveno KJ. Pregnancy outcomes in women with gestational diabetes compared with the general obstetric population. Obstet Gynecol. 1997;90(6):869-873.
- Kim C, Newton KM, Knopp RH. Gestational diabetes and the incidence of type 2 diabetes. Diabetes Care. 2002;25(10):1862-1868.
- Aberg A, Westbom L, Källén B. Congenital malformations among infants whose mothers had gestational diabetes or preexisting diabetes. Early Hum Dev. 2001;61(2):85-95.
- Tennant PW, Glinianaia SV, Bilous RW, Rankin J, Bell R. Pre-existing diabetes, maternal glycated haemoglobin, and the risks of fetal and infant death: a population-based study. Diabetologia. 2014;57(2):285-294.
- Mulla WR. Carbohydrate content in the GDM diet: two views: view 2: low-carbohydrate diets should remain the initial therapy for gestational diabetes. Diabetes Spectr. 2016;29(2):89-91.
- Padayachee C, Coombes JS. Exercise guidelines for gestational diabetes mellitus. World J Diabetes. 2015;6(8):1033-1044.