Importance: Gestational diabetes is associated with several poor health outcomes.

Objective: To update the 2012 review on screening for gestational diabetes to inform the US Preventive Services Task Force.

Data Sources: MEDLINE, EMBASE, and CINAHL (2010 to May 2020), ClinicalTrials.gov, reference lists; surveillance through June 2021.

Study Selection: English-language intervention studies for screening and treatment; observational studies on screening; prospective studies on screening test accuracy.

Data Extraction and Synthesis: Dual review of titles/abstracts, full-text articles, and study quality. Single-reviewer data abstraction with verification. Random-effects meta-analysis or bivariate analysis (accuracy).

Main Outcomes and Measures: Pregnancy, fetal/neonatal, and long-term health outcomes; harms of screening; accuracy.

Results: A total of 76 studies were included (18 randomized clinical trials [RCTs] [n = 31,241], 2 nonrandomized intervention studies [n = 190] 56 observational studies [n = 261,678]). Direct evidence on benefits of screening vs no screening was limited to 4 observational studies with inconsistent findings and methodological limitations. Screening was not significantly associated with serious or long-term harm. In 5 RCTs (n = 25,772), 1-step (International Association of Diabetes and Pregnancy Study Group) vs 2-step (Carpenter and Coustan) screening was significantly associated with increased likelihood of gestational diabetes (11.5% vs 4.9%) but no improved health outcomes. At or after 24 weeks of gestation, oral glucose challenge tests with 140- and 135-mg/dL cutoffs had sensitivities of 82% and 93%, respectively, and specificities of 82% and 79%, respectively, against Carpenter and Coustan criteria, and a test with a 140-mg/dL cutoff had sensitivity of 85% and specificity of 81% against the National Diabetes Group Data criteria. Fasting plasma glucose tests with cutoffs of 85 and 90 mg/dL had sensitivities of 88% and 81% and specificities of 73% and 82%, respectively, against Carpenter and Coustan criteria. Based on 8 RCTs and 1 nonrandomized study (n = 3982), treatment was significantly associated with decreased risk of primary cesarean deliveries (relative risk [RR], 0.70 [95% CI, 0.54-0.91]; absolute risk difference [ARD], 5.3%), shoulder dystocia (RR, 0.42 [95% CI, 0.23-0.77]; ARD, 1.3%), macrosomia (RR, 0.53 [95% CI, 0.41-0.68]; ARD, 8.9%), large for gestational age (RR, 0.56 [95% CI, 0.47-0.66]; ARD, 8.4%), birth injuries (odds ratio, 0.33 [95% CI, 0.11-0.99]; ARD, 0.2%), and neonatal intensive care unit admissions (RR, 0.73 [95% CI, 0.53-0.99]; ARD, 2.0%). The association with reduction in preterm deliveries was not significant (RR, 0.75 [95% CI, 0.56-1.01]).

Conclusions and Relevance: Direct evidence on screening vs no screening remains limited. One- vs 2-step screening was not significantly associated with improved health outcomes. At or after 24 weeks of gestation, treatment of gestational diabetes was significantly associated with improved health outcomes.

Gestational diabetes is diabetes that develops during pregnancy.^1,2 The prevalence of gestational diabetes in the US has typically been estimated at 5.6% to 9.2% when measured from 2007 to 2016^3-6 but may be up to 3-fold higher depending on the diagnostic criteria used.^7,8 Gestational diabetes is usually asymptomatic but is associated with increased risk for several pregnancy and neonatal complications.⁹

In 2014, the US Preventive Services Task Force (USPSTF) recommended screening for gestational diabetes in asymptomatic pregnant women after 24 weeks of gestation (B recommendation).¹⁰ The USPSTF found that evidence was insufficient to screen before 24 weeks of gestation (I statement). This evidence report was conducted to update the 2012 review¹¹ to inform updated USPSTF recommendations.

Scope of Review

Detailed methods and additional study details are available in the full evidence report.⁹ Figure 1 shows the analytic framework and key questions (KQs) that guided the review. KQ5 is addressed only in the full report. KQ3, comparing different screening strategies, was added for this update. This review did not address screening for preexisting or overt diabetes in early pregnancy.

Data Sources and Searches

Ovid MEDLINE and EMBASE, and CINAHL via EBSCOhost, were searched from 2010 to May 22, 2020 (eMethods 1 in the JAMA Supplement). Clinical trial registries and reference lists (including the 2012 review) were reviewed. Ongoing surveillance was conducted to identify major studies published since May 2020 that may affect the conclusions or understanding of the evidence and the related USPSTF recommendation.

Study Selection

Two investigators independently reviewed titles and abstracts, then full-text articles using predefined eligibility criteria (eMethods 2 in the JAMA Supplement). The population for screening and test accuracy was pregnant women without known preexisting diabetes mellitus. For treatment, the population was women with gestational diabetes or hyperglycemia. For benefits and harms of screening, comparative effectiveness of screening approaches, and screening test accuracy, studies using 1-step (diagnostic test only) or 2-step (diagnostic test in women with a positive screening test result) screening strategies at any time during pregnancy were included (eMethods 3 in the JAMA Supplement). In 2-step strategies, the screening test was measurement of fasting plasma glucose level, a 50-g oral glucose challenge test (OGCT), a risk factor–based tool, or glycated hemoglobin (HbA_1c) concentration. For benefits of screening and treatment, comparisons were against no screening or treatment, respectively. For harms of screening, studies comparing outcomes before and after a gestational diabetes diagnosis or comparing women with gestational diabetes aware of their diagnosis vs those unaware were included. To evaluate potential labeling harms, studies on receipt of delivery and perinatal interventions among women diagnosed with gestational diabetes vs those without a diagnosis were included. For accuracy, the reference standard was a currently recommended oral glucose tolerance test (OGTT), mainly using Carpenter and Coustan, the National Diabetes Data Group, or the International Association of Diabetes and Pregnancy Study Group (IADPSG) Consensus Panel diagnostic criteria. Intermediate and health outcomes are listed in Figure 1. Studies had to be published on or after 1995 and conducted in settings applicable to primary care.

Randomized clinical trials (RCTs) and nonrandomized controlled intervention studies were included for screening and treatment; for screening vs no screening, controlled observational studies were also included because of anticipated lack of intervention studies and to assess potential harms. For screening test accuracy, prospective cohort studies in which at least a sample of screen-negative women underwent the reference standard were included. Studies on risk factor strategies or models had to examine a validation cohort

Data Extraction and Quality Assessment

One reviewer abstracted data from the studies; a second reviewer verified accuracy and completeness. Outcomes related to hypertension in pregnancy were classified as preeclampsia, gestational hypertension, or hypertensive disorders in pregnancy (mixed). For cesarean delivery, primary (first) cesarean deliveries were prioritized, but total and emergency cesarean rates were also evaluated. Two reviewers independently assessed the methodological quality of eligible studies using design-specific tools (eMethods 4 in the JAMA Supplement).^13-16 Disagreements were resolved by consensus and, if necessary, consultation with a third reviewer. Studies were rated as “good,” “fair,” or “poor,” based on the seriousness of methodological shortcomings.¹

Data Synthesis and Analysis

For intervention effects using relative risks (RRs), meta-analyses used random-effects models in Review Manager version 5.1 (The Cochrane Collaboration). When moderate or greater statistical heterogeneity (I² ≥ 40%) was observed, sensitivity analysis was performed using the profile likelihood method in Stata version 14.2 (StataCorp); these analyses did not change any of the conclusions, but results are available in the full report⁹ (and for KQ3 are reported in eTables 3 and 4 in the JAMA Supplement). Pooled absolute risk differences (ARDs) were calculated when RRs were statistically significant and for all analyses with at least 1 zero-event study. Heterogeneity was explored with sensitivity analyses using predefined variables (eg, study quality, setting, differing outcome definitions); findings of within study subgroup analyses were extracted.

For diagnostic accuracy, analyses were stratified by timing of the index test in pregnancy and comparison, including different test thresholds. If more than 3 studies were included for a particular comparison, sensitivities and specificities were pooled using bivariate analysis (metandi program in Stata version 14.2) with construction of hierarchical summary receiver operator characteristic curves.

The aggregate strength of evidence was assessed for each outcome, using the Agency for Healthcare Research and Quality methods guidance, based on the number, quality, and size of studies and the consistency and precision of results between studies.¹⁷ Significance testing was 2-tailed; P ≤ .05 was considered statistically significant.

Across the KQs reported in this manuscript, a total of 76 studies were included (18 RCTs [different screening strategies, n = 27,196;^18-24 treatment benefits and harms, n = 4045,^25-35] 2 nonrandomized controlled intervention studies of treatment [n = 190],^36,37 and 56 observational studies [screening benefits, n = 4336;^38-41 screening harms, n = 166,082;^42-48 diagnostic accuracy, n = 91,260^49-93]) (Figure 2). Twenty-three studies were carried over from the prior USPSTF review and 52 new studies were added.

Benefits and Harms of Screening and Different Screening Strategies

Key Question 1. Does screening for gestational diabetes reduce poor health or intermediate outcomes? Does effectiveness vary according to prespecified subgroups?

No RCTs or nonrandomized intervention studies were identified. Four retrospective observational studies (n = 4336)^38-41 compared women who underwent screening for gestational diabetes with women who were not screened (eTable 1 in the JAMA Supplement). Two studies^38,40 from the previous USPSTF review evaluating selected women showed no significant effect of screening; however, sample sizes were small and estimates imprecise. One new study (n = 1012)⁴¹ found 1-step screening of at-risk women was significantly associated with a reduction in late (≥28 weeks of gestation) stillbirth (adjusted odds ratio [OR], 0.68 [95% CI, 0.47 to 0.97]). The other new study (n = 2780)³⁹ found universal 2-step screening, with early screening offered to women with risk factors, significantly associated with fewer cesarean deliveries (RR, 0.78 [95% CI, 0.66 to 0.92]; ARD, –4.8% [95% CI, –8.2% to –1.5%), birth injuries (fracture or dislocation; RR, 0.47 [95% CI, 0.23 to 0.97]; ARD, –0.9% [95% CI, –1.9% to 0.10%]), and admissions to the neonatal intensive care unit (NICU) (RR, 0.67 [95% CI, 0.58 to 0.78]; ARD, –8.7% [95% CI, –12.3% to –5.2%]) compared with historical controls. Prespecified analyses found screening in first trimester was significantly associated with decreased likelihood of NICU admissions vs second-trimester screening but with no significant difference for other outcomes. Both new studies were susceptible to confounding and selection bias.

Key Question 2. What are the harms of screening for and diagnosis of gestational diabetes to the mother, fetus, or neonate?

All 7 studies^42-48 identified for KQ2 were new to this update (eTable 2 in the JAMA Supplement). No significant differences were found in anxiety and depressive symptoms before and after screening for those with negative or false-positive results in 2 cohort studies (n = 1015).^44,48 One study (n = 100)⁴² found that anxiety symptoms scores were slightly higher (6 points on 60-point scale; P = .007) for women with vs without gestational diabetes immediately after receiving results but not significantly higher at gestational week 36 or 6 weeks postpartum.

One good-quality cohort study (n = 3778)⁴⁶ found that the association between macrosomia and cesarean delivery in women with normoglycemia or untreated borderline gestational diabetes was not observed in those with treated gestational diabetes, suggesting that a gestational diabetes diagnosis may have increased the propensity to perform cesarean deliveries. Three large US studies (n = 161,182)^43,45,47 found some differences in hospital experiences (eg, adjusted OR, 0.55 [95% CI, 0.36 to 0.85] for fewer newborns staying in mother’s room) potentially related to labeling because of a gestational diabetes diagnosis. However, there were unmeasured potentially confounding factors such as rates of neonatal hypoglycemia, breastfeeding intentions, and varying hospital policies.

Key Question 3. What is the comparative effectiveness of different screening strategies for gestational diabetes on health and intermediate outcomes? Does comparative effectiveness vary according to prespecified subgroups?

IADPSG vs Carpenter and Coustan Screening

Five RCTs (n = 25,772)^20-24 examined universal screening at 24 to 28 weeks of gestation with the 1-step IADPSG vs 2-step Carpenter and Coustan criteria (Table 1). Three trials were rated fair quality and 2^22,24 good quality. In the largest trial (n = 23,792),²⁰ 25% of women allocated to 1-step screening crossed over to 2-step screening, although results remained similar in an intention-to-treat analysis adjusted for gestational diabetes and adherence. Of the women in this trial’s 2-step group, 1.4% received treatment despite having no diagnosis (only an isolated fasting glucose level ≥ 95 mg/dL), but the authors’ sensitivity analysis for the outcome of large for gestational age showed no evidence that this reclassification affected results. Data from another trial (n = 786)²³ were obtained from a systematic review⁹⁴ and could not be verified.

One-step vs 2-step screening was significantly associated with identification of gestational diabetes in 11.5% vs 4.9% of participants but was not significantly associated with differences in any pregnancy or fetal/neonatal outcome (eTables 3 and 4, eFigures 1-3 in the JAMA Supplement). There was statistical heterogeneity in some analyses in which a fair-quality trial²³ found significant associations favoring 1-step screening, whereas findings between 1 good-quality trial²⁴ and the largest trial (fair quality)²⁰ were similar. In the largest trial, 1-step screening significantly increased risk for neonatal hypoglycemia vs 2-step screening, although this may have been in part due to the routine surveillance of neonates with risk factors including diagnosis of maternal gestational diabetes (eFigure2 in the JAMA Supplement). In 1 trial (n = 921)²⁴ in which all women randomized to 2-step screening underwent the 100-g OGTT (to assist with blinding), 2-step screening was associated with significantly more testing-related adverse events than 1-step screening (eg, reactive hypoglycemia, vomiting, nausea). However, these findings overestimated harms of 2-step screening in clinical practice, in which only women with an abnormal 50-g OGCT result would undergo the 100-g OGTT.

Early vs Usual Timing for Carpenter and Coustan Screening

One good-quality RCT (n = 922)¹⁹ enrolling obese women found early (14 to 20 weeks) vs usual timing of screening with Carpenter and Coustan criteria potentially associated with increased risk of preeclampsia, but the difference was not statistically significant (RR, 1.42 [95% CI, 0.99 to 2.05]; ARD, 4.0% [95% CI, 0.0% to 8.0%]). There were no significant differences for other outcomes, although some estimates were imprecise (eTables 3 and 4 in the JAMA Supplement).

Diagnostic Accuracy

Key Question 4. What is the diagnostic accuracy of commonly used screening tests for gestational diabetes? Does accuracy vary according to maternal subgroup characteristics?

Across 45 prospective cohort studies on diagnostic accuracy, mean sample size was 500 (range, 42-24,854), mean age was 28.8 years (range, 25-32.7), and mean body mass index (BMI, calculated as weight in kilograms divided by height in meters squared) from 22 studies was 24.6 (range, 21.1-28.1). Studies were conducted in 25 countries. Seventeen studies (38%) were rated good quality and 28 (62%) fair quality. No study reported how accuracy varied according to patient characteristics.

50-g Oral Glucose Challenge Test

eFigure 4 in the JAMA Supplement shows findings for the OGCT; results from pooled analyses are summarized in eTable 5 in the JAMA Supplement. Against Carpenter and Coustan criteria, at a 140-mg/dL cutoff, the pooled sensitivity and specificity (8 studies, n = 6190)^{53,60,69,73,76,81,83,90} were 81.9% (95% CI, 68.3% to 90.4%) and 81.8% (95% CI, 71.2% to 89.1%), respectively. Against the National Diabetes Data Group criteria (6 studies, n = 5375),^{58,60,67,72,81,88} the 140-mg/dL cutoff had a sensitivity of 85% (95% CI, 72.0% to 92.6%) and specificity of 81.2% (95% CI, 75.9% to 85.6%). Using a 135-mg/dL cutoff (4 studies, n = 1554)^60,73,76,83 resulted in higher sensitivity (93.3% [95% CI, 23.7% to 99.8%]; reference, Carpenter and Coustan criteria) but lower specificity (78.9% [95% CI, 53.3% to 92.5%]) than the 140-mg/dL cutoff. At a cutoff of 130 mg/dL, findings against Carpenter and Coustan criteria were inconsistent from 3 studies (n = 1034) (eFigure 4 in the JAMA Supplement).^60,76,83 Sensitivity of the OGCT against IADPSG criteria was low across all cutoffs in 2 good-quality studies (n = 2091; eFigure 4 in the JAMA Supplement);^55,71 at a 140-mg/dL cutoff, specificity in those 2 studies was 81% and 93%.

Fasting Plasma Glucose

Against Carpenter and Coustan criteria, fasting plasma glucose at a cutoff of 85 mg/dL was associated with sensitivity of 88% (95% CI, 84% to 91%) and specificity of 73% (95% CI, 46% to 90%) and at a cutoff of 90 mg/dL with sensitivity of 81% (95% CI, 75% to 85%) and specificity of 82% (95% CI, 61% to 93%) (3 studies, n = 2233) (eTable 5 in the JAMA Supplement).^50,76,83 Sensitivity was greater than 90%, although specificity was low (<47%), at cutoffs of 80 mg/dL or less (4 studies; n = 6781).^50,73,76,83 Against IADPSG criteria, at 24 weeks of gestation or later, fasting plasma glucose testing with cutoffs of 80 mg/dL or less was associated with high sensitivity (most estimates >90%) but low-specificity (5 studies; n = 52,532).^{52,74,80,92,93}

HbA_1c Concentration

Screening with HbA_1c concentration was not associated with both high sensitivity and specificity at any threshold (18 studies).^{51,54,56,57,63,64,66,70,74,75,77,78,82,85,86,88,89,91} Screening with HbA_1c at 24 weeks of gestation or after had sensitivity greater than 90% at cutoffs of 4.5% to 5.0% (Carpenter and Coustan [1 study; n = 430]⁵¹ and National Diabetes Data Group [1 study; n = 114]⁸⁵) or 4.6% to 4.7% (IADPSG [2 studies; n = 819]).^66,82 In a good-quality study (n = 1158),⁵⁴ early screening using 4.5% to 4.8% HbA_1c cutoffs was associated with sensitivity greater than 95% vs National Diabetes Data Group criteria at 24 weeks of gestation or after.

Risk-Based Screening

Single studies found different risk-based tools (some in combination with measurement of fasting plasma glucose level) associated with sensitivities of 83% to 98% against Carpenter and Coustan (n = 341),⁵³ National Diabetes Data Group (n = 3131),⁸¹ or IADPSG (n = 258)⁶² criteria; however, specificity was highly variable (17% to 80%).

Benefits and Harms of Treatment

Key Question 6. Does treatment of gestational diabetes during pregnancy reduce poor health and intermediate outcomes? Does effectiveness vary according to maternal subgroup characteristics?

Eleven RCTs (n = 4045)^25-35 and 2 nonrandomized controlled intervention studies (n = 190)^36,37 addressed treatment of gestational diabetes. Mean sample size was 326 (range, 21-1000), mean age was 29.2 years (range, 26.3-32.6), and mean BMI was 28.4 (range, 22.9-34.5) (Table 2). Four studies^27,28,32,34 were rated good quality and the others fair quality.

Treatment at 24 to 28 Weeks of Gestation

Like the prior USPSTF review, 2 large good-quality RCTs (n = 1958)^27,32 contributed a substantial proportion (40%-90%) of the events for many analyses. Four new studies were added^28,31,35,36 and 6 new publications^95-100 for 1 large previously included trial³² provided data for long-term outcomes or subgroup analyses. Based on trial inclusion criteria, findings are most applicable to adult women identified using 2-step screening, though there were some differences across trials in eligibility criteria, baseline glycemia, and treatment protocols (Table 2). Apart from 1 trial²⁹ that did not report data, weeks of gestation at delivery was similar between groups in all trials.

Treatment of gestational diabetes was significantly associated with lower risk of primary cesarean deliveries vs no treatment (3 studies; RR, 0.70 [95% CI, 0.54 to 0.91]; I² = 0%; ARD, −5.3% [95% CI, −10.3% to −0.24%]).^25,32,36 Treatment was also associated, though not significantly, with fewer preterm deliveries (4 studies; RR, 0.75 [95% CI, 0.56 to 1.01]; I² = 0%; ARD, −2.6% [95% CI, −4.9% to 0.02%])^31,32,35,36 (Figure 3). There was no significant association but marked inconsistency for preeclampsia (Figure 4; 6 studies^{25,28,31,32,35,36}) and hypertensive disorders in pregnancy (3 trials^27,32,35); findings appeared sensitive to inclusion of a trial³⁵ from a country not rated as “very high” on the Human Development Index (Figure 4). Treatment was not significantly associated with reduced risk of gestational hypertension (2 trials;^32,35 some imprecision), total cesarean deliveries (8 trials^{25-29,31,32,35}), emergency cesarean deliveries (1 trial²⁷), induction of labor (5 trials^{25,27,28,32,35}), or maternal birth trauma (2 studies^27,36).

For fetal/neonatal outcomes, treatment was significantly associated with lower risk of shoulder dystocia (4 trials; RR, 0.42 [95% CI, 0.23 to 0.77]; I² = 0%; ARD, −1.3% [95% CI, −4.3% to −1.6%]),^25,27,32,35 macrosomia (8 studies; RR, 0.53 [95% CI, 0.41 to 0.68]; I² = 42%; ARD, −8.9% [−12.0% to −5.9%]),^{25-27,29,31,32,35,36} LGA (7 trials; RR, 0.56 [95% CI, 0.47 to 0.66]; I² = 0%; ARD, −8.4% [95% CI, −10.8% to −6.1%]),^{26-28,31,32,35,36} and NICU admissions (5 trials; RR, 0.73 [95% CI, 0.53 to 0.99]; I² = 0%; ARD, −2.0% [95% CI, −4.5% to 0.5%]).^{26,28,31,32,36} Treatment was significantly associated with reduced risk of birth injury (eg, fracture or nerve palsies) in 3 trials that reported at least 1 event (OR, 0.33 [95% CI, 0.11 to 0.99]; I² = 0%)^27,28,32 but not when including 4 zero-event trials (ARD, −0.2% [95% CI, −0.6% to 0.2%]).^{27-29,31,32,35,36} There was no significant association between treatment and risk of mortality (6 trials),^{27-29,32,35,36} respiratory distress syndrome (2 trials),^27,32

Key Question 7. What are the harms of treatment of gestational diabetes, including severe maternal and neonatal hypoglycemia, delivery of neonates who are small for gestational age, and poor long-term growth and development outcomes in the child?

Treatment offered at 24 weeks of gestation or later was not significantly associated with increased risk of SGA (6 trials; n = 2646; RR, 1.10 [95% CI, 0.83 to 1.47]).^{25-27,31,32,36} No trial reported on the association between treatment and poor long-term growth and development outcomes in childhood. Findings from small RCTs of early treatment vs usual care were imprecise or did not report harms (eg, maternal hypoglycemia).

The findings in this evidence report are summarized in Table 3. Direct evidence on the benefits of screening vs no screening remains limited and consists of observational studies with methodological limitations. Few studies reported on harms from screening or a diagnosis of gestational diabetes and those available were limited by imprecision and methodological limitations. There were no significant associations between screening using 1-step IADPSG vs 2-step Carpenter and Coustan criteria, but some statistical heterogeneity was present (especially for neonatal hypoglycemia) and estimates were heavily weighted by 1 large trial²⁰ that accounted for 92% of patients.

Treatment vs no treatment was associated with reduced risk for some pregnancy and several neonatal/fetal outcomes. Findings are most applicable for hyperglycemia identified using 2-step screening approaches and to adult (vs adolescent) women with singleton pregnancies and without chronic hypertension or previous gestational diabetes. Most of the treatment interventions relied on frequent self-monitoring of blood glucose levels and clinic visits to monitor glucose targets, which could reduce applicability of findings to women with limited or no insurance coverage, health care access, or ability to perform self-monitoring. Results for cesarean delivery and labor induction are difficult to interpret because of differences in delivery practices. Findings are sparse for long-term health outcomes from treatment and for all outcomes from early treatment. No trial of treatment at 24 weeks of gestation or after used oral medications; therefore, potential medication harms would not have been captured.

This review differs from the 2012 USPSTF review¹¹ by including additional evidence on potential harms of screening and gestational diabetes diagnosis; evaluating comparative effectiveness of different screening strategies; and relying on more rigorous inclusion criteria and applicable comparisons for test accuracy. Although findings were generally consistent with those from the prior review, there are some differences. New evidence resulted in increased certainty regarding the accuracy of fasting plasma glucose and HbA_1c levels as screening tests and the association between treatment and improved outcomes, including reduced risk of NICU admissions. Additional information on preeclampsia and NICU admissions was obtained from authors of 1 trial,²⁷ enhancing handling of these data. Several publications from one of the larger treatment trials³² provided new evidence regarding lack of effect for several subgroups and long-term outcomes. For the new KQ on comparative effectiveness, several trials were located including 3 large trials^19,20,24 and 1 very large trial²⁰ from the US examining highly applicable comparisons. The greater prevalence in gestational diabetes diagnosis resulting from 1-step IADPSG vs 2-step Carpenter and Coustan screening, without associated benefits, suggests potential overdiagnosis and overtreatment. In addition, the 1-step approach requires additional resources related to having all women undertake a 2-hour OGTT and provision of counseling and treatment to more women.

Evaluating the effectiveness of screening vs no screening remains heavily reliant on indirect evidence about test accuracy and treatment effects. Although evidence on diagnostic accuracy is useful for assessing which screening tests may be most useful in a 2-step approach, reliance on these tests alone would result in a high number false-positive results (especially using lower cutoffs with high sensitivity), particularly in general-prevalence populations (eTables 6 and 7 in the JAMA Supplement). In addition, the applicability of treatment trials to women diagnosed with gestational diabetes using the OGCT as a stand-alone test is uncertain. Ongoing trials of treatment for women with positive OGCT screening results but not gestational diabetes,¹⁰³ and for those with gestational diabetes by IADPSG criteria but excluding those with 2 abnormal glucose values,¹⁰⁴ would be useful to further inform assessment of treatment benefits among women with lesser degrees of dysglycemia.

Limitations

This review had several limitations. First, only English-language studies were included.¹⁰⁵ Second, graphical and statistical tests for small sample effects were not conducted because all analyses included fewer than 10 trials.¹⁰⁶

Third, the DerSimonian and Laird random-effects model was used to pool studies, which may result in CIs that are too narrow, particularly when heterogeneity is present.¹⁰⁷ However, results were similar when analyses were repeated using the profile likelihood method. Fourth, the observational studies included for KQs for which trials were lacking were susceptible to unmeasured confounding and other methodological limitations.

Fifth, some studies were conducted in countries in which screening and treatment for gestational diabetes, as well as management of pregnancy, may differ from that in the US. However, this review focused on screening and diagnostic criteria used in the US, and results appeared consistent across geographic settings. Sixth, data on how the effects of screening and treatment varied according to patient characteristics such as race/ethnicity, age, and other socioeconomic factors were very limited. Seventh, studies that applied older definitions for gestational diabetes or that did not screen for preexisting diabetes² may have included some women with overt diabetes, who are expected to have worse outcomes.¹⁰⁸

Direct evidence on screening vs no screening remains limited. One vs 2-step screening was not significantly associated with improved health outcomes. At or after 24 weeks of gestation, treatment of gestational diabetes was significantly associated with improved health outcomes.

Source: This article was first published online in the Journal of the American Medical Association on August 10, 2021 (JAMA. 2021;326(6):539-562. doi:10.1001/jama.2021.10404).

Conflict of Interest Disclosures: Dr Donovan reported being coauthor of the Diabetes Canada 2018 Evidence-based Pregnancy Guidelines and receiving nonfinancial support from Medtronic. No other disclosures were reported.

Funding/Support: This research was funded under contract HHSA 290201500009-I, Prism Order HHSA29032014T, from the Agency for Healthcare Research and Quality (AHRQ), US Department of Health and Human Services, under a contract to support the US Preventive Services Task Force (USPSTF).

Role of the Funder/Sponsor: Investigators worked with USPSTF members and AHRQ staff to develop the scope, analytic framework, and key questions for this review. AHRQ had no role in study selection, quality assessment, or synthesis. AHRQ staff provided project oversight, reviewed the report to ensure that the analysis met methodological standards, and distributed the draft for peer review. Otherwise, AHRQ had no role in the conduct of the study; collection, management, analysis, and interpretation of the data; and preparation, review, or approval of the manuscript findings. The opinions expressed in this document are those of the authors and do not reflect the official position of AHRQ or the US Department of Health and Human Services.

Additional Contributions: We thank AHRQ Medical Officers Justin Mills, MD, MPH, and Iris Mabry-Hernandez, MD, MPH, and the USPFTF for their contributions to this project. We thank Tina Korownyk, MD (University of Alberta), for contributions during topic development, and Robin Featherstone, MLIS, and Diana Keto Lambert, MLIS (University of Alberta), for development of searches for the topic development and review stages, respectively. We also acknowledge past and current USPSTF members who contributed to topic deliberations. The USPSTF members, external reviewers, and federal partner reviewers did not receive financial compensation for their contributions.

Additional Information: A draft version of this evidence report underwent external peer review from 9 federal partners representing the Centers for Disease Control and Prevention; Indian Health Service, Office of Clinical and Preventive Services, Division of Diabetes Treatment and Prevention; National Institutes of Health, Division of Intramural Population Health Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development; National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Diseases; Division of Health Promotion and Communication, Office of Disease Prevention and Health Promotion; Office of Research on Women’s Health; and 5 content experts (Andrew Garrison, MD, University of Utah; Joseph R. Biggie Jr, MD, Ochsner Health, New Orleans, Louisiana; Diane Farrar, PhD, Bradford Institute for Health Research, Bradford, United Kingdom; Florence M. Brown, MD, Joslin Diabetes Center, Boston, Massachusetts; Linda A. Barbour, MD, University of Colorado School of Medicine at Anschutz Medical Campus). Reviewer comments were presented to the USPSTF during its deliberation of the evidence and were considered in preparing the final evidence review.

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See the USPSTF Procedure Manual¹² for information about analytic frameworks. KQ indicates key question.
^a No assumptions will be made about whether hyperglycemia discovered early in pregnancy (eg, in first trimester) is gestational diabetes or some other form; gestational diabetes will include all women with hyperglycemia but not meeting criteria for overt diabetes at any time during pregnancy.
^b Using 2-step (screening first and, when indicated, diagnostic tests second) or 1-step (diagnostic tests only) strategies, each based on various criteria and thresholds, and offering treatment to patients diagnosed with gestational diabetes.

^a Forty-one studies included in the prior US Preventive Services Task Force (USPSTF) review were excluded for this update, largely because they were observational studies on treatment (n = 6) and studies on accuracy (n = 35) that did not use a predefined reference standard or did not test at least a sample of women with the reference standard. All details for key question (KQ) 5 are in the full report.⁹

Details of each analyses, including study-level data and weighting, are available in the full report.⁹ VHDI indicates Very High Human Development Index Country.

All risk ratios from Mantel-Haenszel random-effects model.

Abbreviations: BMI (calculated as weight in kilograms divided by height in meters squared); CDE, certified diabetes educator; FPG, fasting plasma glucose; HbA_1c, glycated hemoglobin; IADPSG, International Association of Diabetes in Pregnancy Study Groups; NR, not reported; OGCT, oral glucose challenge test; OGTT, oral glucose tolerance test; RCT, randomized clinical trial; SMBG, self-monitoring of blood glucose; wGA, weeks of gestation.
^a Risk factors included BMI 30 or greater, previous gestational diabetes, history of macrosomic infant (>4 kg), or polycystic ovarian syndrome.

Abbreviations: BMI, body mass index; FBG, fasting blood glucose; FPG, fasting plasma glucose; HbA_1c, glycated hemoglobin; IADPSG, International Association of Diabetes and Pregnancy Study Groups; IQR, interquartile range; NR, not reported; OGCT, oral glucose challenge test; OGTT, oral glucose tolerance test; RBG, random blood glucose; RCT, randomized clinical trial; SGA, small for gestational age; SMBG, self-monitoring blood glucose; wGA, weeks of gestation; WHO, World Health Organization.
SI conversion factor: To convert glucose values from mmol/L to mg/dL, divide by 0.0555.
^a Calculated as weight in kilograms divided by height in meters squared.

Abbreviations: ARD, absolute risk difference; BMI, body mass index (calculated as weight in kilograms divided by height in meters squared); FPG, fasting plasma glucose; HbA_1c, glycated hemoglobin; IADPSG, International Association of Diabetes and Pregnancy Study Groups; KQ, key question; LGA, large for gestational age; NDDG, National Diabetes Data Group; NGT, normal glucose tolerance; NICU, neonatal intensive care unit; OGCT, oral glucose challenge test; OGTT, oral glucose tolerance test; OR, odds ratio; RCT, randomized clinical trial; RR, relative risk; SGA, small for gestational age.
SI conversion factor: To convert glucose values to mmol/L, multiply by 0.0555.