In a managed care plan with a large number of women with GDM pregnancies, we found that between 1995 and 2006, screening for postpartum diabetes increased from 20.7 to 53.8%. The increase in screening performance is not likely to be due to advancing maternal age or changes in the racial/ethnic composition of women with GDM, as this trend in screening performance was similar after adjustment for age and race/ethnicity, and almost the entire population of pregnant women was screened for GDM between 1995 and 2006. Although the proportion of women with IFG on their postpartum screen did not significantly change over time, the proportion of women with diabetes (diagnosed by FPG levels) at postpartum decreased by ~50%. This observed decrease in diabetes among women with postpartum screening is not likely to be a consequence of the small increase (3%) in GDM screening over time. The decrease is more likely because of better identification of diabetes before pregnancy, as suggested by the reported increase in postpartum screening among women with GDM and because of an increase in glucose screening in postpartum women without GDM (1.9% in 1995 vs. 8.2% in 2006).
As in other reports (5
), the majority of women in our cohort did not undergo postpartum diabetes screening in the early years of the study. Asian and Hispanic women were more likely to undergo postpartum screening. It is possible that health care providers might have recommended more postpartum screening among these racial/ethnic groups, given their higher prevalence of diabetes (19
). It is also possible that Asian women were more likely to have had a recent physical examination, giving the health care provider the opportunity to recommend screening, as suggested by racial/ethnic differences in access to care among GDM women (20
). Similar to other reports, we found that greater contact with medical care, either through a postpartum visit or other contacts, was associated with greater postpartum screening and may have provided additional opportunities to perform screening (6
). Women who were more likely to be screened also were older and had higher educational attainment. Although reasons are speculative, these women may have had greater awareness of their diabetes risk and the recommendation for screening. In women who were screened postpartum, GDM was diagnosed earlier in their index pregnancy, and they were more likely to have been treated with medications, which may have increased their and their provider's awareness of their diabetes risk. Glucose levels on the diagnostic 3-h OGTT during pregnancy were similar in women who were and were not screened, suggesting that these were not used to guide testing. As shown by others (21
), there was a suggestion that some of the women with a history of GDM who might have had a higher risk of developing diabetes during the postpartum period, such as those who were obese or with higher parity, were less likely to perform postpartum screening.
The American Diabetes Association (16
), the American College of Obstetricians and Gynecologists (17
), and the Fifth International Congress Workshop for Gestational Diabetes (15
) endorse the postpartum OGTT and FPG to different extents. If only FPG were used in postpartum screening, 74 (40%) cases of IGT and 16 (75%) cases of diabetes would have been missed. Kitzmiller et al. (19
) reported that among 527 women with GDM, at postpartum 16.5% had isolated IGT, only 16% of women in whom diabetes was diagnosed met the criteria for both elevated FPG and 2-h values, and 21 of 25 women met the criteria for diabetes according to their 2-h values alone. Hunt and Conway (21
) also reported that one-third of their postpartum GDM cohort undergoing the OGTT and who had diabetes or pre-diabetes had isolated 2-h elevations. Their results are very similar to those found in this study: 78 of 204 women compared with 41 of 117 (or 38% vs. 35%). Therefore, the greater convenience of the FPG needs to be weighed carefully against its decreased sensitivity, particularly among women with a history of GDM.
This report has several limitations. We were not able to distinguish whether the lack of screening occurred because of a lack of provider order or other reasons. Such a distinction might have implications for interventions to improve screening performance. However, provider orders for screening might occur only after negotiation with the patient, and a lack of provider order may, at least in part, reflect women's objections to the test. We defined obesity by using race/ethnicity-specific percentiles, rather than height-to-weight ratios, thus introducing the possibility for misclassification and artificially decreasing the association between obesity and screening to the null. Information on other confounders, such as family history of diabetes, was not available from electronic records.
Because the population of women with GDM is of reproductive age, postpartum screening and subsequent diagnoses of diabetes affect not only the mothers but also future pregnancies. The risk of complications, particularly stillbirths and congenital abnormalities, may be reduced with optimal glycemic control before the subsequent pregnancy (1
). Prepregnancy glycemic control might also reduce the risk of the infant to the in utero exposure to hyperglycemia that might lead to childhood obesity and diabetes (22
). A diagnosis of pre-diabetes would identify women at high risk of future maternal diabetes, but this risk could be reduced through the application of interventions such as thiazolidinediones, metformin, or intensive lifestyle modification (3
We conclude that, among women with a GDM history, postpartum diabetes screening has increased, but screening is still suboptimal. Performance of an FPG alone, as opposed to the OGTT, will miss a subpopulation of women at risk. Interventions that increase postpartum screening performance are needed.