In a large-scale, multicenter study, we found 21% persistent glucose intolerance within 1 year after a pregnancy with GDM in Caucasian women. However, we saw that the return rate was different at the three study sites. We suspect that the return rate might have been influenced by the population composite and the care setting. Based on identified risk factors, we developed an algorithm for postpartum glucose testing that allows us to target women who should be intensively followed and motivated to return for testing because of their high risk for abnormal glucose tolerance. A combination of ≥2 risk factors, which was present in 40% of the population, was highly predictive for the development of diabetes within 1 year after delivery, and 86% of diabetes would be detected.
The prevalence of abnormal glucose testing observed in our population was within the range reported from other studies. The prevalence of isolated IFG varies between 3 and 6%, the prevalence of IGT varies between 7 and 29%, and the prevalence of diabetes varies between 5 and 12% (4
). Particular risk factors associated with abnormal postpartum glucose tolerance varied among studies, but early diagnosis of GDM and high maternal BMI as potential signs of preexisting insulin resistance and insulin use as a marker of the degree of hyperglycemia had been proven to be predictive in most of the studies. Age, prior GDM, family history of diabetes, weight gain, or neonatal macrosomia often lost their predictive value when maternal glucose values were included in the multivariate analysis (1
). We identified four independent antenatal risk factors; besides maternal BMI >30 kg/m2
, gestational age at diagnosis <24 weeks, and insulin use, a 1-h glucose value >200 mg/dl increased the risk by almost threefold. There is controversy in the literature over whether the antenatal fasting (7
) or postchallenge values (10
), or both (18
), or the number of abnormal values of an OGTT (13
) is more predictive for postpartum diabetes. Similar to our data, in one of the large studies that included almost 3,000 women, the 1-h OGTT value was proven to be superior to the fasting glucose value (11
). Recent data from Canada demonstrated lower postpartum insulin sensitivity in women with an isolated abnormal 1-h glucose value compared with those with only elevated 2- or 3-h high values (21
). The postchallenge hyperglycemia reflects the first-phase release. Insulin clamps during pregnancy in women with GDM showed that a low first-phase intravenous glucose tolerance test response is independently associated with a high risk for type 2 diabetes within 6 months after delivery (14
The presence of almost 22% abnormal glucose tolerance within the 1st year after GDM underlines the importance of early postpartum testing. Despite the knowledge that after GDM women have a substantial risk of staying glucose intolerant or developing diabetes with the highest conversion rate in the 1st years after the index pregnancy (3
), physician and patient compliance for early postpartum glucose testing is low. Only 20% of the obstetricians, even in an academic medical center, ordered postpartum diabetes screening tests for their patients (22
). With a few exceptions (11
), most studies reported a return rate less than or ~50% (7
Overall, 51% of the women in our study returned for testing, but we noted a remarkable diversity between the study sites that might be influenced by the social and ethnic composition of the population. The highest recall rates were achieved in the setting of a private clinic in an urban middle-class population, whereas in a community obstetrical hospital in an underprivileged Berlin district with a high rate of immigrants (41.2%) only 23% of all women returned for testing and only 13% of women with Turkish or Arabian background returned. On the patient side, it is likely that different overall health awareness and increased family obligations in large families may contribute to low testing rates. Unfortunately, it seems that, especially in populations with high prevalence of postpartum glucose intolerance, many obstacles have to be overcome. Some of these are related to the health system, some are internal to the patient, and some are socioeconomic or cultural.
An algorithm to target women at high risk for postpartum glucose intolerance might ensure that the majority of postpartum diabetes is identified. Ideally, it should be possible to calculate the individual risk of each woman for diabetes during the early postpartum period based on easily available antenatal risk factors. Based on the prevalence of abnormal ppOGTTs according to the number of risk factors present, we defined three risk categories. Women with low risk (OR 1.3) had a low prevalence of abnormal ppOGTTs (11%), whereas in women with intermediate or high risk we expect to see 36% with persistent glucose intolerance. These women accounted for 40% of our population, but the rate of women at high risk may vary in other populations depending, for example, on the obesity and underlying type 2 diabetes prevalence. If our model of risk factor–based postpartum screening holds in other populations, we would detect 86% of postpartum diabetes by focusing on intensive counseling and following women who are likely to remain diabetic. Concentrating our efforts on motivating these women to return for testing and developing a system of cooperation with other caregivers, e.g., the pediatrician who sees the children, might reduce the number of missed cases of postpartum diabetes. Missing the opportunity to identify pre-diabetes or diabetes in underserved women may mean that diabetes is not identified until a much later stage than in women who access health care.
The limitation of our study is that we do not have information about the postpartum glucose tolerance status of all of the women who did not return for postpartum testing. We have relatively complete data for two centers, but because of the low return rates in Berlin, the incidence of abnormal ppOGTTs might be overestimated. Because nonreturners at the site with a low return rate were not different from returners regarding risk factors for diabetes we consider our results to be representative for the whole population. However, further studies with prospective use of our model in different populations have to be conducted to prove the validity and transferability of our data.
Considering the high rate of early glucose intolerance, it is imperative that we ensure that women who develop GDM understand that glucose intolerance may persist or return after pregnancy and that this risk for diabetes can be modified by lifestyle changes (6
), and, therefore, postpartum testing is essential. However, widespread implementation of ppOGTT is difficult. The model of risk assessment we presented, which is based on easily available antenatal data, may allow us to target women with a high need of intensive motivation for postpartum testing and therefore may offer a chance to reduce the number of missed cases of postpartum diabetes in women with recent GDM.