Current clinical management and research on medical nutrition therapy for gestational diabetes mellitus in Australia: is it too glucocentric?

Barnes, Robyn Ann

Title: Current clinical management and research on medical nutrition therapy for gestational diabetes mellitus in Australia: is it too glucocentric?
Creator: Barnes, Robyn Ann
Relation: University of Newcastle Research Higher Degree Thesis
Resource Type: thesis
Date: 2022
Description: Research Doctorate - Doctor of Philosophy (PhD)
Description: Introduction: Gestational diabetes mellitus (GDM) is a form of diabetes of varying severity, with onset or first recognition during pregnancy. GDM has been found to increase the risk of several adverse maternal and neonatal outcomes including large for gestational age (LGA) infants, caesarean birth and neonatal hypoglycaemia. The traditional approach to GDM management largely focuses on monitoring and treatment of maternal hyperglycaemia. Medical Nutrition Therapy (MNT) (1, 2) is the first line of treatment, with insulin commenced if MNT is not sufficient to achieve glycaemic targets. However, there are significant gaps in evidence regarding the optimal MNT for GDM. It is possible that other clinical non-glycaemic variables may contribute to variations in therapeutic and pregnancy outcomes. Pre-pregnancy body mass index (BMI) and excessive maternal weight gain may drive increasing insulin resistance and further exacerbate maternal hyperglycaemia. Aim: The aim of this thesis was to determine whether pre-pregnancy BMI and maternal weight gain explain variations in therapeutic (insulin therapy or MNT only) and neonatal outcomes (including caesarean delivery, early delivery, large-for-gestational-age (LGA) infants and small-for-gestational-age infants) and therefore should be included in future research, clinical management and risk-based models of care in women with GDM. Five research questions were developed to achieve this overarching aim. Results are presented by research question below. Methods: Five studies were conducted. A national online cross-sectional survey of dietitians was conducted to explore current dietetic practice in the management of MNT, and whether weight gain advice and monitoring is provided. Four retrospective cohort study analyses were conducted using de-identified prospectively collected clinical data in the Bankstown-Lidcombe Hospital Diabetes Centre Database System (DCDS) (1992-2019). These studies investigated the relationship between pre-pregnancy BMI, maternal weight gain, and therapeutic and neonatal outcomes in women with singleton pregnancies who were diagnosed with GDM. The Australasian Diabetes in Pregnancy Society 1998 criteria were used to diagnose GDM in the first three cohort studies. This involved a two-step process with an initial screening 50-gram glucose challenge test, proceeding to a 75-gram oral glucose tolerance test (OGTT) if 1-hour BGL ≥ 7.8 mmol/L. GDM was diagnosed using a 75-gram OGTT if a fasting blood glucose level (FBGL) was ≥ 5.5 mmol/L and/or 2-hour BGL was ≥ 8.0 mmol/L. The fourth study diagnosed GDM by universal screening in a one-step process using the World Health Organization (WHO) diagnostic criteria. Diagnostic criteria using a 75-gram OGTT are one or more abnormal value/s: ≥5.1 mmol/L fasting, ≥10.0 mmol/L at 1 hour, or ≥8.5 mmol/L at 2 hours. Results: Research question 1: What is current dietetic clinical practice for the nutritional management of GDM in Australia, and is weight management advice included? The survey of dietitians (n=152) found, similar to a survey conducted in 2009, that most dietitians provide nutrition education related to carbohydrate frequency, distribution, quantity, and glycaemic index (GI). However, recommendations regarding minimum daily carbohydrate amounts (40-220 grams) and the percentage of energy from carbohydrate were widely variable (30-65%). Encouragingly, there was an increase in provision of gestational weight gain advice to 59% [(n=61/103) in 2019 versus 40% reported in 2009 [(n=77/195); p<0.05]. Few, however, reported that recommended carbohydrate amounts were based on ‘desired maternal weight gain’ (21.7%, n=33). The findings of this survey suggested that the primary focus of dietary education for GDM was carbohydrate intake, which appeared to be prioritised over advice to achieve recommended maternal weight gain. Research question 2: What independent clinical or laboratory variables could predict the likelihood of insulin therapy and/or adverse outcomes, and do they include pre-pregnancy BMI? The second cohort study of 3317 singleton pregnancies was from women diagnosed with GDM from 1992-2015. Analysis identified seven dichotomised significant independent predictors of insulin therapy: maternal age >30 years, family history of diabetes, pre-pregnancy obesity (BMI ≥30 kg/m2) prior GDM, early diagnosis of GDM (<24 weeks gestation), fasting venous BGL ≥5.3 mmol/l, and HbA1c at GDM diagnosis ≥5.5% (≥37 mmol/mol). Requirement for insulin in addition to MNT could be estimated according to the number of predictors present where 85.7%-93.1% of women with 6-7 predictors required insulin compared to 9.3%-14.7% of women with 0-1 predictors. Pre-pregnancy BMI ≥30 kg/m2 was an independent predictor of insulin therapy and several adverse outcomes in this model. Research question 3: What impact do pre-pregnancy BMI and maternal weight gain before and after GDM diagnosis have on the likelihood of an infant being born SGA or LGA? The first cohort study analysis was of 1695 singleton pregnancies from women with GDM from 1994-2009. This analysis found that significant independent predictors of LGA infants were: weight gain before GDM treatment initiation, pre-pregnancy BMI, weight gain after GDM treatment initiation, and treatment type, but not HbA1c at GDM presentation or smoking. Significant predictors of SGA infants were: weight gain before and after GDM treatment initiation, but not pre-pregnancy BMI, HbA1c at GDM presentation, or smoking. Research question 4: Are excessive gestational weight gain (EGWG) at first presentation with GDM, and continued excessive gestational weight gain (cEGWG) after commencing GDM management independently associated with increased risk of insulin therapy and the likelihood of LGA infant birthweight? The third cohort study of 3281 singleton GDM pregnancies (1992-2015) found that 776 women had excessive gestational weight gain (23.6%). This was defined as exceeding the upper limit of Institute of Medicine (IOM) recommended maternal weight gain target ranges for the entire pregnancy at of GDM presentation ≥18.1kg (BMI ≤18.5kg/m2); ≥16.1kg (18.5-24.9kg/m2); ≥11.6kg (25.0-29.9kg/m2); ≥9.1kg (≥30.0kg/m2). Women with excessive gestational weight gain had higher mean oral glucose tolerance fasting plasma glucose (FPG) (27.7 ± 4.2 weeks gestation) after adjustment for confounders (5.2 mmol/L [95% confidence intervals (CI) 5.1-5.3] versus 5.0 mmol/L [95% CI 4.9-5.0], p<0.01) and increased initiation of insulin therapy (47.0% versus 33.6%, p<0.0001) with adjusted odds ratio (aOR) 1.4 (95% CI 1.1-1.7, p<0.01). For each 2 kg increment of continued excessive gestational weight gain, there was a 1.3-fold increased use of insulin therapy [95% CI 1.1-1.5], p<0.001, an 8-unit increase in final daily insulin dosage [95% CI 5.4-11.0], p<0.0001, and a 1.4-fold increase in LGA [95% CI 1.2-1.7], p<0.0001. Excessive gestational weight gain independently increases OGTT FPG. Continued excessive gestational weight gain in GDM increases the risk of LGA infants and insulin requirements. Research question 5: Will the addition of weight management to GDM management result in improved maternal and neonatal outcomes? The fourth cohort study was an analysis in women with singleton pregnancies diagnosed with GDM from 2016-2019. At the time of commencing GDM management, all women (n=1034) were provided with personalised weight targets (PWT) for the remainder of the pregnancy. These weight targets were personalised according to pre-pregnancy BMI, weeks’ gestation and weight already gained. Logistic regression analysis found that women who exceeded their PWT had significantly higher mean insulin doses (28.8 ± 21.5 units vs 22.7 ± 18.7, p=0.006) and a higher rate of LGA infants (19% versus 9.8%, p<0.001), with an adjusted odds ratio (aOR) of 1.99 ([95% CI 1.25-3.15], p=0.004 than women who achieved their PWT. There was no difference in rates of SGA infants in those who achieved versus exceeded their PWT (5.3% versus 8.0%) (aOR 0.77 [95% CI 0.41-1.44], p=0.41). Those who gained below their PWT had lower rates of LGA infants compared to women who achieved their PWT (aOR 0.48 [95% CI 0.25-0.95], p=0.034), but concurrently had increased rates of SGA infants (aOR 1.9 [1.19-3.12], p=0.008). These findings suggest that weight management after gestational diabetes diagnosis appears to provide additional benefits to glucose-lowering treatment. Conclusions: As this body of research shows, pre-pregnancy BMI and maternal weight gain before and during GDM management independently contribute to insulin requirements and risk of LGA and SGA infants. Findings from this thesis suggest that MNT would benefit from a greater focus on individualisation of energy intakes to achieve maternal weight gain recommendations. The overall findings from this body of research show that pre-pregnancy BMI and maternal weight gain contribute to variations in therapeutic and neonatal outcomes and therefore should be included in future research, clinical management, and risk-based models of care in women with GDM.
Subject: gestational diabetes mellitus; maternal weight gain; therapeutic and pregnancy outcomes; large for gestational age infants
Identifier: http://hdl.handle.net/1959.13/1513767
Identifier: uon:56767
Language: eng

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