Among the membership of a large managed health care plan with a high prevalence of GDM, approximately one-half of women identified as having GDM had postpartum glucose testing in the 6 months after delivery. The majority of women (79%) tested in the 6 months postpartum had an FPG only. Only one-half of women who had postpartum glucose testing had their tests during the 6- to 12-week postpartum period recommended by the ADA. Postpartum testing and timing of testing were associated with demographic, clinical, and health care–related factors. Women whose treatment included insulin alone or insulin plus oral hypoglycemic agents had the same odds of being tested postpartum as those whose treatment did not include any pharmacologic agents. However, individuals treated with oral agents alone had lower odds for being tested than those who did not receive pharmacotherapy during pregnancy.
Of the women tested, a relatively small proportion (~1%) met the criteria for diabetes, while a greater proportion (~16%) had IFG and/or IGT. However, detection of IFG/IGT or diabetes was independently and positively associated with having been treated with insulin or oral agents during pregnancy and timing of postpartum glucose testing. While women tested between 12 weeks and 6 months postpartum had higher mean FPG during pregnancy compared with those tested in the early and ADA-recommended windows, the association between being tested in the later period and having abnormal results postpartum persisted after controlling for the prenatal FPG value.
The observation that women not tested postpartum had higher fasting and 3-h values during pregnancy suggests that if a larger number of women had been tested postpartum, a greater proportion of the entire sample of GDM women would have been found to be glucose intolerant postpartum. Furthermore, 79% were tested by FPG only. If a 75-g OGTT postpartum test had been consistently administered, the prevalence of diagnosed diabetes would most likely have increased (20
). Of the women in our sample who had an OGTT postpartum with normal FPG results, 8% had IGT or diabetes based on their 2-h value.
Postpartum glucose testing
There has been significant heterogeneity across studies that have examined rates and correlates of postpartum glucose testing after GDM with respect to calendar years studied, time between delivery, and postpartum testing population (hospital-based samples [12
] versus managed care [15
]) and the approach used to identify women with GDM. The present study included all women who met the ADA criteria for GDM based on the results from the 100-g OGTT test performed during pregnancy, since ICD-9 codes alone was found to be an unreliable means of identifying women with GDM in our health plan database (2
). Indeed, while 16% of the women identified as having GDM based on their prenatal 100-g OGTT results did not have a discharge diagnosis of GDM, over one-third (38.5%) of these women had postpartum glucose testing. In spite of the differences and consistent with the present study, approximately half of the women with GDM in the earlier studies underwent postpartum testing (12
Of the studies that examined GDM pharmacological treatment in relation to whether or not postpartum testing was performed, two found a positive association (14
), one found a negative association (13
), and one found no association (15
). In the present study, we found that while 50.3% of the women with no pharmacotherapy and 51.1% of the women on insulin were tested, only 42.6% of women on oral agents had postpartum glucose testing. Given that the women who took oral agents only or insulin during their GDM pregnancy and received postpartum testing were 40 or 57% as likely to have IFG/IGT and two to three times as likely to have diabetes, respectively, as women not treated with these medications, women who require pharmacotherapy to control their blood glucose during pregnancy should be tested in the postpartum period.
Postpartum test results
In the three other studies reporting the results of postpartum glucose testing (12
), the prevalence of diabetes ranged from 2 to 8% compared with 1% reported in the present study. Additionally, the prevalence of IFG and/or IGT ranged from 11 to 33%, compared with 16% in the present study. In the two studies (12
) that used the same ADA criteria to identify women as having GDM in their clinical center as were used in the present study, 72% of those tested for glucose intolerance in one of the centers had an OGTT postpartum (13
) compared with only 21% in the present study. This may have resulted in a higher proportion of women identified as having impaired glucose regulation in their population. One study used the higher NDDG blood glucose threshold (21
) to identify women with GDM and included tests conducted from 6 weeks through 1 year postpartum (16
). Either or both of these factors may have accounted for the higher prevalence of impaired glucose regulation in their population compared with our findings.
Limitations and strengths
We were unable to assess the occurrence of postpartum glucose testing among the ~15% of women with GDM who disenrolled from the health plan within 6 months after their deliveries. We could not determine whether women were advised by a health care professional to have postpartum testing or whether the test was ordered but not completed, since this information is not retained in the laboratory database during the study period. We could also not determine if the patient received a reminder to report for testing by mail or telephone. Thus, missed tests could be a result of lack of physician orders or women not returning for postpartum testing. Additionally, we were not able to explore the associations between obesity, postpartum testing, and ongoing glucose abnormalities in the postpartum period because maternal height and weight were not available in clinical databases or the California birth certificates for the period of this study.
The strengths of this study include the use of multiple clinical and administrative databases to identify and characterize women with GDM, including pharmacotherapy for GDM during pregnancy from a diverse insured cohort and to determine whether members of that cohort had been tested for glucose abnormalities postpartum. Because 95% (n = 11,187) of the women in the sample had KPSC prescription drug coverage during pregnancy, we were able to examine the associations requiring anti-hyperglycemic agents, postpartum testing, and test results with a high level of accuracy. Our sample included all women from 1999 through 2006 identified as having GDM using a standard laboratory test (100-g 3-h OGTT) using ADA criteria to assess the presence of GDM. Additionally, we were able to identify those women found to have IGT/IFG and those having a provisional diagnosis of diabetes using the results of their 75-g OGTT and FPG tests done during the postpartum period and to describe the demographic, clinical, and health service utilization characteristics of those women.
Testing for ongoing glucose dysregulation after a GDM-affected pregnancy may allow the opportunity for clinical interventions to reduce the risk of developing diabetes or treatment to reduce the risk of diabetes-related complications among women found to have diabetes (22
). The risk of pregnancy-related complications among women with diabetes, a population that is growing (2
), may be reduced by optimal use of preconception care (24
). The findings from this and other studies suggest that the rates of postpartum glucose testing after GDM are suboptimal. Rates of postpartum glucose testing after GDM pregnancies may be increased by incorporating alerts into electronic medical records so that postpartum glucose testing orders are automatically generated or physician-generated. Automated live or recorded telephone or e-mail messages could also be used to remind women to obtain testing after the tests are ordered. Postpartum glucose testing is an important first step in attempting to prevent both recurrence of GDM and the development of nongestational diabetes subsequent to a pregnancy complicated by GDM.