Gestational diabetes (GDM) is a potentially serious disorder requiring timely diagnosis and management to prevent adverse maternal and fetal outcomes. Of increasing concern today, when treating the woman with GDM, is the need to provide every woman with an intensive management plan to optimise the likelihood of favourable pregnancy outcomes. Early identification of those women with GDM who require insulin therapy in addition to diet therapy would be beneficial in the planning and standardisation of clinical management protocols, to enhance pregnancy outcomes and increase cost benefits with improved allocation of resources. The aim of this study was to evaluate the ability of the fasting plasma glucose level (FPG) at diagnosis to predict an increased risk to the fetus and the need for insulin therapy in a pregnancy complicated by GDM. A prospective longitudinal study design and recruitment by convenience sample was used. Data were obtained from 327 women and their babies. Diagnosis of GDM was made by a 75 gram oral glucose tolerance test (OGTT) using Australasian Diabetes in Pregnancy Society (ADIPS) criteria with the exception of seven women diagnosed on a blood glucose level >11.1mmol/l. Following consent of the women data were collected by a self report questionnaire and the medical record system at three points; at first intervention, following delivery and at the postpartum OGTT. Demographic, social, medical, maternal and neonatal outcome data were collected. The management protocol was similar for all of the women. Following nutritional intervention any woman who could not meet the glycemic targets of <= 5mmol/l fasting and/or <= 6.5mmol/l two hours postprandial was commenced on insulin therapy. The women had a mean age of 32 years, body mass index (BMI) of 25.7 and parity of 2 (range 1-12). Diagnosis was made at an average of 30 weeks and 70 women required insulin therapy with a mean dose of 34 IU per day, commencing at a mean of 31 weeks gestation. Mean birthweight was 3400G. Of the babies 12% were >4000G. Congenital abnormalities occurred in 3%, neonatal morbidities in 2% and there was 1 death in utero. Logistic regression analysis found the following significant associations: Increasing maternal BMI was related to increasing FPG levels at diagnosis and the requirement of higher insulin doses. There was a negative linear relationship to weight gain. Ethnicity was associated with maternal BMI and ethnicity with BMI was associated with birthweight in the specific ethnic group. BMI with insulin therapy as a covariate and the FPG value at OGTT were predictive of persistent glucose intolerance in 14% of women postpartum. Each value of the OGTT was a significant predictor of the need for insulin therapy as a function of the week of gestation. The FPG level was the statistical model of best fit. A 50% probability for requiring insulin was reached with a FPG at diagnosis of 4.0 mmol/l if tested at 10 weeks gestation, 5.1mmol/l at 20 weeks and 6.1 mmol/l at 30 weeks (p<.001). These results support the substantive research aim of the study. The model has the power to predict the probability (risk) of requiring insulin therapy based on the maternal FPG level at the OGTT according to the week of gestation. The study results demonstrate that glucose intolerance is linked to a number of adverse maternal and fetal outcomes in a continuous and graded fashion. The degree of reversibility of maternal and fetal risk through therapeutic interventions such as nutrition therapy, blood glucose monitoring, exercise and active patient participation aimed at improving glucose tolerance is unknown. Therefore, the rationale for, and feasibility of, new treatment strategies such as the application of this statistical model as a management approach require large scale randomised intervention studies, oriented toward measuring maternal and fetal outcomes amongst different populations.