Effect of gestational diabetes mellitus on maternal thyroid function and body mass index

Background: The exact influences of thyroid functions on body mass index (BMI) are ill-defined in euthyroid pregnant women with gestational diabetes mellitus (GDM). Objectives: To investigate the effect of GDM on maternal thyroid functions and BMI. Methods: :  A case- control study was conducted in Saad Abualila Hospital, Khartoum, Sudan June to August 2015. Cases included women with GDM and healthy pregnant women as controls. Thyroid hormones [thyroid-stimulating hormone (TSH), free tri-iodothyronine (FT3), and free thyroxine (FT4)] and anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin (anti-TG) antibodies were measured. Results: :  BMI was significantly increased in GDM patients (26.3 (2.7) Kg/m 2 ) compared with the control group (24.3(1.8) Kg/m 2 , P = 0.001). Levels of FT3 and FT4 were significantly decreased in GDM patients (0.632 (0.408 ─ 1.074) pg/ml; 0.672 (0.614 ─ 0.960) ng/dl) compared with the healthy pregnant women (0.820 (0.510─1.385) pg/ml, P = 0.021; 0.840 (0.767─1.200) ng/dl, P < 0.001). In contrast, anti-TPO and anti-TG were significantly higher in GDM patients (11.13 (7.969 ─13.090) IU/ml; 14.40 (10.91─20.69) IU/ml) compared with the control group (8.90 (6.375─10.48 IU/ml, P = 0.022; 10.50 (8.2─13.95) IU/ml, P = 0.010). BMI correlated negatively with FT3 ( r = ─ 0. 375, P = 0.002) and FT4 ( r = ─ 0. 316, P = 0.009) and positively with anti-TPO ( r = 0.361, P = 0.002) and anti-TG ( r = 0.393, P = 0.010). Conclusion: The present results add further evidence for decreased free thyroid hormones, increased anti-thyroid autoantibodies and higher BMI in patients with GDM compared to healthy pregnant women. BMI correlated directly with FT3 and FT4, but failed to demonstrate significant association with TSH.