An Evaluation of the Second Trimester Thyroid Function Test in Gestational Diabetes Mellitus: A Case-Control Study

Introduction: Gestational diabetes mellitus (GDM) is defined as glucose intolerance in a female with its onset or first recognition during pregnancy. Females with GDM are at higher risk of developing antenatal complications like preeclampsia during pregnancy and increased risk of type 2 diabetes as well as cardiovascular disorders later in their life. Maternal thyroid changes in the first and second trimesters of pregnancy have been widely related to the risk of GDM. Hypothyroidism during pregnancy is associated with early and late complications like abortions, anaemia, gestational hypertension, placental abruption and postpartum haemorrhage, impaired infant neurodevelopment, and low birth weight. Objectives: This study aims to compare the thyroid function test (TFT) (serum fT3, fT4, TSH) and thyroid peroxidase antibody (anti TPO) between GDM and non GDM pregnant women in the second trimester and to correlate the adverse pregnancy outcomes with TFT in GDM and non GDM women. Methods: A nested case-control study was done in the Department of Obstetrics and Gynaecology, Department of Endocrinology, Department of Paediatrics, University College of Medical Sciences, and Guru Teg Bahadur (GTB) Hospital, Delhi. About 350 pregnant women from 13 weeks till 28 weeks period of gestation were screened out of which 40 GDM and 40 non GDM women were selected after performing an oral glucose tolerance test (OGTT). A TFT and anti TPO test were compared between GDM and non GDM participants. Furthermore, various parameters like sociodemographic profile, mode of delivery, pregnancy outcomes, and adverse maternal and adverse neonatal outcomes were compared. Conclusion: The mean age of GDM women is found to be more than non GDM women. The mean TFT values are significantly lower in women with GDM as compared to non GDM women. In addition, higher values of anti TPO antibody (thyroid autoantibody) were found in the GDM group which aids in insulin resistance. Maternal complications like polyhydramnios, preterm labour, and pregnancy-induced hypertension were found to be more frequent in the GDM group compared to the non GDM group, but the results were statistically not significant. There was a higher incidence of caesarean delivery in the GDM group. Thus, we recommend the implementation of routine thyroid function profile testing in all antenatal females especially those who are at risk of developing GDM. Our study is one of the few Indian studies to evaluate the association of TFT in GDM, and we recommend similar research with a larger sample size and postnatal follow-up.