An observational study to determine the incidence of thyroid dysfunction among pregnant women in Northern Tasmania : effect of thyroid status on maternal, foetal and neonatal outcomes

This thesis comprises four chapters; Literature Review, Materials and Methods, Results and Discussion/Conclusions. It represents the work conducted by the candidate during the period April 2013 and May 2015. Chapter one is a critical review of the scientific literature related to iodine and iodine deficiency. Firstly, it highlights that Tasmania has had a history of thyroid disease in the community, including iodine deficiency. More recently, a Tasmanian study reported that children born to iodine-deficient mothers suffered impaired cognitive development. Secondly, it examines the changes occur in thyroid function during pregnancy and whether these have any influence on pregnancy outcomes. It further analyses different opinions regarding the role of iron in pregnancy as well as the effect of iron deficiency anaemia on pregnancy. It also explores the feasibility of iodine level surveillance in childbearing women as well as potential applications of cord blood in foetal thyroid assessment. Studies of thyroid function and iron deficiency during pregnancy in Tasmania are limited. Furthermore, the application of general screening for thyroid function/dysfunction during and prior to pregnancy remains controversial. Thus, the overall aim of the present study was to determine the incidence of thyroid dysfunction during pregnancy and to investigate whether any possible relationships exist between low thyroid status and complications occurred during pregnancy and labour. Chapter two summarises the study design, subject recruitment, materials, and methods used during this study. It further describes sample processing, tests used during screening, including full blood count, iron studies, maternal, foetal thyroid function tests (TSH, FT4, FT3 and anti-thyroid peroxidase antibodies), and urinary iodine concentration. The results chapter primarily presents the data of the study in a series of tables and figures, including description of the study population and study outcomes. A response rate of 28.9% was demonstrated, with 609/636 (95.7%) of participants successfully screened for thyroid status. Next, incidence of thyroid abnormalities in the study population was demonstrated; 22 (9 with TSH >3 mU/L, 13 with TSH 2.5-3mU/L) and 75 with FT4<8.93.4%, representing 3.4% of low thyroid status and 12.3% of isolated hypothyroxinemia, respectively. Furthermore, possible association of maternal and foetal complications with the thyroid status was also shown; prolonged labour (IRR 3.31; 95% CI 1.13 to 9.69; P<0.05) and gestational diabetes (IRR 1.69; 95% CI 0.55-5.25; P=0.36). It also demonstrates that the study population is iodine deficient; median UIC=117˜í¬¿g/L with 11.2% of them having developed isolated hypothyroxinemia (FT4<8.9 mU/L) during pregnancy. Additionally, CB-TSH results of 402/615 (65%) of babies born to this study cohort was analysed. It shows a significant decrease of TSH level in the cord blood of babies born to participants with bleeding complications (APH/IPH) (Mean (SD) 4.91(2.16); 95% CI -5.48 to -2.48; P<0.001) compared to CB-TSH of babies born to participants without bleeding (Mean (SD) 9.40(5.97)). Although this may not reflect abnormal foetal thyroid function, it does demonstrate a strong thyroid reaction to maternal ante-/intra-partum bleeding that needs further investigations. The last chapter discusses the main outcomes of the study and shows how the incidence of low thyroid function of this study is unexpectedly low but in line with international figures. It also discusses the importance of iodine surveillance as well as general screening for thyroid function prior or at early pregnancy. The chapter concludes by emphasising the importance of the incidence of thyroid disorder in this population in Northern Tasmania, and the possibility of an increased incidence of antenatal complication in association with low thyroid status being equivocal. Since the main limitation of this study was the small sample size, more statistically significant outcomes are anticipated with larger scale studies in the future.