Screening, diagnosis and lifestyle intervention program for gestational diabetes mellitus in an urban primary health clinic in South Africa

Dickson, Lynnsay M
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We investigated the feasibility of implementing a universal screening program for gestational diabetes mellitus (GDM) in an urban low resource setting, using glucometers rather than a calibrated laboratory to measure blood glucose concentrations of the 75 g oral glucose tolerance test (OGTT). In this prospective, pragmatic, cross-sectional study, 592 consecutive women underwent an OGTT at 24–28 weeks’ gestation. The World Health Organization (2013) diagnostic thresholds were applied. Five plasma-calibrated glucometer brands were evaluated against two independent laboratories, which used either the glucose oxidase (GOx) or hexokinase (HK) method to measure plasma glucose levels. Also, retrospectively, the validity of a universally applied fasting plasma glucose (FPG) of  4.5 mmol/l was evaluated against a risk factor assessment, which is current standard care, as a method of screening for GDM. In addition, as part of formative work to develop an intervention that may be applied locally, the experience of women previously affected by GDM was examined through a series of focus group discussions (FGD). In this qualitative component of this study, the Diabetes Conversation Map educational instrument was used to examine the experiences of women previously affected by GDM, and these FGD were recorded, transcribed and thematically analysed. GDM prevalence determined by the glucometers was 12.7%. Three of the five glucometer brands evaluated were within the predetermined total allowable error, but only at fasting of the OGTT. All glucometers were inaccurate at one and two hours. Glucometer results were significantly positively biased relative to both laboratories results at all time points of the test, meaning, they potentially over-diagnosed GDM. GDM prevalence determined by GOx and HK methods were 6.9% and 5.1% respectively. Unexpectedly, there was a significant bias of 0.20 mmol/l between laboratories, with a low agreement of 34% on GDM positive diagnoses. The absence of a true gold standard, and the ambivalent results provided by the calibrated laboratories that served as the reference test, created clinical diagnostic uncertainty in determining participants GDM status. Nevertheless, an elevated fasting glucose of  5.1 mmol/l defined  80% of GDM positive diagnoses by all methods of measurement. The use of a universally applied FPG (GOx laboratory method served as reference) would mean 25.8% of women would be identified as medium to high risk and would need to undergo a complete OGTT and 97.6% of GDM affected women would be identified. If risk factor based selective screening were applied, only 34.6% of women would require an OGTT, however, 43.9% of GDM positive cases would have been missed. Results of the qualitative study suggested women affected by GDM reacted with shock, anxiety, confusion, and disbelief to their diagnosis of GDM. They were aware of inconsistent diagnostic procedures applied at clinics and hospitals. Despite difficulty adjusting to a diet initially perceived to be unpalatable and more expensive, changing to a healthier lifestyle was considered an overall positive consequence of their diagnosis. Lifestyle changes were partially retained postpartum and were reported to have a positive effect on other family members. Unexpectedly, women reported that being HIV (Human Immunodeficiency Virus) positive was preferable and less stressful than having GDM. In conclusion, the thesis research found that there is no ideal method to measure plasma glucose concentrations of the OGTT in a low resource setting. Reliance on routine laboratory methods to measure blood glucose concentrations of the OGTT may miss GDM positive women. Acknowledgement of the limitations of the different methods of measurement is an important consideration when developing GDM screening strategies. In this study population, FPG measured by glucometers may be a superior screening strategy for GDM, over the current practice of selective screening with a laboratory-dependent OGTT. Regarding women’s experience of GDM, consistency in health messaging, diagnostic criteria and diagnostic procedures will be essential to a successful roll out of GDM screening in low resource South Africa settings
A thesis submitted to the Faculty of Health Sciences, University of Witwatersrand, in fulfilment of the requirements for the degree of Doctor of Philosophy (PhD), Johannesburg, South Africa, 2020