Background
Less than one-half of women with gestational diabetes mellitus are screened for type 2 diabetes postpartum. Other approaches to postpartum screening need to be evaluated, including the role of screening during the delivery hospitalization.
Objective
To assess the performance of an oral glucose tolerance test administered during the delivery hospitalization compared with the oral glucose tolerance test administered at a 4- to 12-week postpartum visit.
Study Design
We conducted a combined analysis of patient-level data from 4 centers (6 clinical sites) assessing the utility of an immediate postpartum 75-g oral glucose tolerance test during the delivery hospitalization (PP1) for the diagnosis of type 2 diabetes compared with a routine 4- to 12-week postpartum oral glucose tolerance test (PP2). Eligible women underwent a 75-g oral glucose tolerance test at both PP1 and PP2. Sensitivity, specificity, and negative and positive predictive values of the PP1 test were estimated for diagnosis of type 2 diabetes, impaired fasting glucose, or impaired glucose tolerance.
Results
In total, 319 women completed a PP1 screening, with 152 (47.6%) lost to follow-up for the PP2 oral glucose tolerance test. None of the women with a normal PP1 oral glucose tolerance test (n=73) later tested as having type 2 diabetes at PP2. Overall, 12.6% of subjects (n=21) had a change from normal to impaired fasting glucose/impaired glucose tolerance or a change from impaired fasting glucose/impaired glucose tolerance to type 2 diabetes. The PP1 oral glucose tolerance test had 50% sensitivity (11.8–88.2), 95.7% specificity (91.3–98.2%) with a 98.1% (94.5–99.6%) negative predictive value and a 30% (95% confidence interval, 6.7–65.3) positive predictive value for type 2 diabetes vs normal/impaired fasting glucose/impaired glucose tolerance result. The negative predictive value of having type 2 diabetes at PP2 compared with a normal oral glucose tolerance test (excluding impaired fasting glucose/impaired glucose tolerance) at PP1 was 100% (95% confidence interval, 93.5–100) with a specificity of 96.5% (95% confidence interval, 87.9–99.6).
Conclusion
A normal oral glucose tolerance test during the delivery hospitalization appears to exclude postpartum type 2 diabetes mellitus. However, the results of the immediate postpartum oral glucose tolerance test were mixed when including impaired fasting glucose or impaired glucose tolerance. As a majority of women do not return for postpartum diabetic screening, an oral glucose tolerance test during the delivery hospitalization may be of use in certain circumstances in which postpartum follow-up is challenging and resources could be focused on women with an abnormal screening immediately after the delivery hospitalization.
Gestational diabetes mellitus (GDM) is a metabolic complication of pregnancy, affecting 2%–16% of all pregnancies in the United States. GDM is hyperglycemia diagnosed during pregnancy when the progressive increases in insulin resistance cannot be adequately accommodated by an additional pancreatic β-cell response. Among women with a GDM-affected pregnancy, the postpartum prevalence (4–20 weeks after delivery) of impaired glucose tolerance (IGT) is 17%–23% and type 2 diabetes (DM) is 5%–14%. The American Congress of Obstetricians and Gynecologists recommends that all women with a GDM-affected pregnancy have a 2-hour, 75-g oral glucose tolerance test (OGTT) performed at 4–12 weeks’ postpartum to screen for disorders of glucose metabolism, including DM. However, less than one half of women with GDM receive postpartum OGTT screening. Multiple barriers exist to receiving postpartum screening, such as lack of a physician order for the postpartum glucose test, failure by the woman to obtain the glucose test, and loss of health insurance. Factors associated with poor follow-up include low education, lack of awareness for risks of DM, low health literacy, and public insurance.
Why was this study conducted?
Few women with gestational diabetes mellitus, completing the postpartum screening for type 2 diabetes is recommended. Other screening approaches, including the utility of an immediate screen for diabetes during the delivery hospitalization, need to be evaluated.
Key findings
A normal oral glucose tolerance test result during the delivery hospitalization appears to exclude type 2 diabetes. The performance of the delivery oral glucose tolerance test was mixed when evaluating other outcomes, including impaired fasting glucose or impaired glucose tolerance.
What does this add to what is known?
These data suggest an oral glucose tolerance test during the delivery hospitalization may reasonably exclude type 2 diabetes. However, the limitations of the immediate postpartum oral glucose tolerance test need to be considered and further evaluated. An oral glucose tolerance test during the delivery hospitalization may be appropriate in certain populations or low-resource centers where follow-up after discharge is challenging.
To reduce barriers to postpartum glucose testing and improve compliance, and because the optimal timing of testing has not been determined definitively, both American Congress of Obstetricians and Gynecologists and the American Diabetes Association recently have extended the time window for postpartum testing from 6–12 weeks to 4–12 weeks. However, limited data support the rationale for waiting until 4–12 weeks postpartum to screen for DM. Recently, several studies published compared the relationship between a 75-g OGTT at the delivery hospitalization and at the traditional 6 weeks’ postpartum among women who had GDM. The results across these studies showed high sensitivity and specificity for diabetes from the OGTT performed during the delivery hospitalization. Yet, all of these studies were underpowered due to poor follow-up for the recommended 4- to 12-week OGTT. Therefore, the purpose of this study was to combine individual patient-level data across 6 centers to report sensitivity, specificity, and positive predictive values (PPVs) and negative predictive values (NPVs) of a delivery hospitalization 75-g OGTT compared with the gold standard 4- to 12-week 75-g OGTT for the diagnosis of DM, IGT, and impaired fasting glucose (IFG).
Materials and Methods
We conducted a combined analysis of patient-level data collected from 2012 to 2016 at 4 centers (6 clinical sites) that evaluated the results of an immediate postpartum 75-g OGTT during the delivery hospitalization (PP1) for the diagnosis of DM when compared with a routine 4- to 12-week postpartum OGTT (PP2) for women who had GDM during their pregnancy. We analyzed previously collected data from Women & Infants Hospital, Providence, RI; Johns Hopkins Hospital, Baltimore, MD; MetroHealth Medical Center and University Hospital, Cleveland, OH; Washington University Medical Center, Saint Louis, MO; and New York University-Winthrop, Mineola, NY. Each center had variable inclusion, exclusion, and diagnostic criteria (see Supplemental Table 1 for a complete description of inclusion, exclusion, and diagnostic criteria for GDM ). For this combined analysis, we limited the dataset to women who had a complete OGTT at PP1 and PP2. In addition, as all centers had a high rate of loss to follow-up, characteristics of study eligible women with a PP1 visit who were lost to follow-up (defined as absent PP2 testing) were compared with women who completed both study visits to evaluate for potential bias. To improve compliance, some centers offered stipends (MetroHealth and University Hospitals) or gift cards (Women & Infants Hospital) once patients completed all postpartum OGTT testing. Each institution obtained approval from their respective institutional review boards.
Each study center contributed deidentified data on maternal demographic and clinical information, including medical history, height, prepregnancy weight (self-reported), body mass index, medication use, delivery date, maternal weight at delivery, gestational weight gain, maternal and infant health at delivery (including newborn weight and mode of delivery), postpartum tobacco use, and breastfeeding status at discharge. Prepregnancy weight and total gestational weight gain were not available for either MetroHealth or University Hospital, and tobacco use was not available for Johns Hopkins Hospital. Demographic data were compared by center of enrollment for all women meeting inclusion into the final analysis. Significant differences were assessed via χ 2 tests or analysis of variance as appropriate. Furthermore, the Fisher exact test was used to assess differences where χ 2 tests were not sufficient due to small cell size in comparison groups. A P value of <.05 was considered significant.
Based on the 75-g OGTT, we used the American Diabetes Association criteria for defining IGT, IFG, and DM. IGT was defined as having a 2-hour value of 140–199 mg/dL, and IFG was defined as having a fasting blood glucose of 100–125 mg/dL. DM was defined on postpartum OGTT as a fasting value ≥126 mg/dL or 2-hour value ≥200 mg/dL. The results of the OGTT for all centers were dichotomized in 2 ways: any glucose intolerance (IFG, IGT, or DM) or those with only DM. We estimated the sensitivity, specificity, PPV, and NPV with 95% confidence intervals (CIs) for a diagnosis of DM (vs IFG/IGT/normal) and for any glucose intolerance (IFG/IGT/DM vs normal) for OGTT results during delivery hospitalization (PP1) compared with 4- to 12-weeks postpartum (PP2). Furthermore, we estimated the sensitivity, specificity, PPV, and NPV with 95% CIs for a diagnosis of DM (vs normal only) for OGTT results at PP1 compared with PP2. Finally, we estimated unadjusted odds ratios with 95% CIs using logistic regression to determine which maternal factors are related to an abnormal OGTT at PP2 among women who had a normal OGTT at PP1.
Results
When data from all 6 centers were combined, 319 women completed a PP1 screening; 152 were lost to follow-up for the PP2 OGTT (47.6%). Table 1 presents maternal demographic data by each enrolling center for the 167 women who completed both a PP1 and a PP2 visit for our analysis. Although mean age at enrollment was not significantly different across centers, race/ethnicity, education, prepregnancy weight, weight at delivery, frequency of cesarean delivery, and frequency of breastfeeding were significantly different among centers. In addition, a disproportionate number of women with an abnormal PP2 OGTT were enrolled in Ohio (n=35, MetroHealth and University Hospital). Loss to follow-up ranged from 17% to 71%. When we compared the women lost to follow-up with those who completed both PP1 and PP2 study visits ( Supplemental Table 2 ), significant differences were noted in the frequency of loss to follow-up by center of recruitment and gestational age at delivery. In addition, women lost to follow-up had a lower mean 2-hour glucose level result on the PP1 OGTT compared with women who completed both study visits.
| Characteristic | Aggregate across all 4 centers N=167 | Women and Infants and Johns Hopkins N=47 | New York University-Winthrop N=24 | MetroHealth and University Hospital N=67 | Washington University N=29 | P value a |
|---|---|---|---|---|---|---|
| Mean age at enrollment, y | 31.8 | 31.6 | 34.4 | 31.1 | 31.6 | .1 |
| Race/ethnicity (%) | <.0001 b | |||||
| White | 31.7 | 40.4 | 16.7 | 31.3 | 31.0 | |
| African American | 37.1 | 25.5 | 12.5 | 52.2 | 41.4 | |
| Hispanic | 15.6 | 10.6 | 37.5 | 10.5 | 17.2 | |
| Asian | 11.4 | 12.8 | 33.3 | 4.5 | 6.9 | |
| Other | 4.2 | 10.6 | N/A | 1.5 | 3.5 | |
| Education, % c | .02 b | |||||
| Less than high school | 10.9 | 5.3 | 25.0 | 9.2 | N/A | |
| High school | 31.8 | 21.1 | 20.8 | 43.1 | N/A | |
| More than high school | 57.4 | 73.7 | 54.2 | 47.7 | 100.0 | |
| Nulliparous, % | 34.1 | 44.7 | 33.3 | 35.8 | 13.8 | .05 |
| Mean prepregnancy weight, kg d , e | 81.3 | 83.1 | 69.3 | N/A | 91.6 | .006 |
| Prepregnancy body mass index, % f | .1 b | |||||
| Normal weight (18.5–<25 kg/m 2 ) | 25.8 | 24.4 | 37.5 | N/A | 15.0 | |
| Overweight (25–<30 kg/m 2 ) | 23.6 | 20.0 | 33.3 | N/A | 20.0 | |
| Obesity (30+ kg/m 2 ) | 50.6 | 55.6 | 29.2 | N/A | 65.0 | |
| Mean weight at delivery, kg g | 97.5 | 93.2 | 83.6 | 99.5 | 112.2 | .003 |
| Mean gestational weight gain, kg e | 13.9 | 10.3 | 14.3 | N/A | 21.4 | .08 |
| Medication for glucose control during pregnancy, % | 54.5 | 48.9 | 66.7 | 49.3 | 65.5 | .2 |
| Mean gestational age at delivery, wk | 38.4 | 38.5 | 38.7 | 38.5 | 37.8 | .06 |
| Cesarean delivery, % | 47.9 | 34.0 | 45.8 | 46.3 | 75.9 | .005 |
| Breastfeeding at discharge, % | 76.7 | 89.4 | 87.5 | 70.2 | 62.1 | .01 |
| Tobacco use postpartum, % h | .08 b | |||||
| Users | 16.7 | N/A | 8.3 | 23.9 | 6.9 | |
| Non-users | 83.3 | N/A | 91.7 | 76.1 | 93.1 | |
| Mean time from delivery to immediate PP OGTT, d (range) | 2.2 (1.0–5.0) | 2.0 (2.0–2.0) | 2.5 (2.0–4.0) | 2.1 (1.0–5.0) | 2.6 (1.0–4.0) | .0002 |
| Mean time from delivery to late PP OGTT, d (range) | 55.0 (24.0–196.0) | 53.5 (24.0–95.0) | 61.5 (40.0–196.0) | 54.9 (38.0–90.0) | 51.6 (34.0–83.0) | .3 |
| Loss to follow-up (has complete PP visit 1 but no complete PP visit 2) (%) | 47.7 | 51.6 | 71.1 | 17.3 | 50.0 | <.0001 |
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