Factors Affecting Thyroid Volume Of Pregnant Women In Non-High Water Iodine Concentration Areas Of Tianjin

ObjectiveAs a well indicator reflecting long-term iodine status,thyroid volume(TV)is affected by many factors other than iodine status.However,the effects of several factor was controversial.Moreover,there is little knowledge of the change of TV after pregnancy in Chinese iodine-replete pregnant women and the main reason were also debatable.Our objective was to explore factors affecting TV of pregnant women in areas of non-high water iodine concentration,aimed to provide more evidence for the confounding factors when TV was used to evaluate the iodine status and to infer the reason of TV change during pregnancy in the condition of iodine replete.MethodsA cross-sectional survey was conducted in Tianjin.Healthy pregnant women during the second trimester aged 25 to 30 years were selected.Basic information,like name,age,weight currently and before pregnant,gestational weeks,number of pregnancy and parturition,smoking,drinking were recorded by a questionnaire.Ultrasonographic TV was measured and then caculated total goiter rate(TGR).Urine iodine concentration(UIC)and urine creatinine concentration of spot urine sample were measured.Fasting blood sample was collected and the concentration of serum thyroid stimulating hormone(TSH),free triiodothyronine(FT3),free thyroxine(FT4),Serum thyroid peroxidase antibody(TPOAb)and thyroglobulinantibody(TGAb)were detected.The associations of these factors and TV were analysed.Results1.400 pregnant women during second trimester were included.The weight,BSA and BMI currently were all significantly higher than those values before pregnancy(The P values were all less than 0.001).2.The median UIC was156.6(102.1-227.8)?g/L.The median TV was 10.3(8.5-12.4)ml and the TGR was 2.6%.Only 1.43% pregnant women were diagnosed as thyroid dysfunction and all were subclinical hypothyroidism.3.TV was positively correlated with age(rs=0.113,P=0.018),BMI before pregnancy(rs=0.222,P<0.001),current BMI(rs=0.254,P<0.001),BSA before pregnancy(rs=0.263,P<0.001)and current BSA(rs=0.292,P<0.001).Overweight or obese pregnant women had larger TV.TV and TGR became larger with increasing current BSA.Women whose weight gain after pregnancy had the same TV and current BSA compared with women whose weight not gain.But the BSA before pregnancy was lower.TV and TGR were higher in higher age group.4.TV was not significantly correlated with UIC(rs=0.000,P>0.05)and UI/Cr(rs=-0.082,P>0.05).And TV was not significantly different in different UIC groups.TV was negatively correlated with TSH(rs=-0.299,P<0.001),positively correlated with FT3(rs= 0.196,P<0.001),and not significantly correlated with FT4(rs= 0.037,P>0.05).TV and TGR had increasing trends with decreasing TSH.5.TV was not significantly different in pregnant women exposed to tobacco smoke or not,and in pregnant women with different pregnancy or parturition number.6.TV was larger in pregnant women with positive TPOAb.TV and TGR were both higher in pregnant women with positive TGAb.Goiter pregnant women had higher age,current BSA,positive rate of TGAb and lower TSH than normal ones.7.Age,current BSA,TSH,positive TPOAb and TGAb were significant predictors in the multiple liner regression analysis.Current BSA and TSH were major factors according to the standardized regression coefficients.Age,TSH and positive TGAb were significant in the logisitic regression analysis.TSH(b=-1.577,OR=0.207)and positive TGAb(b=2.193,OR=8.960)may were stronger risk factors of goiter.Conclusion1.In non-high water iodine concentration areas,TSH and BSA during pregnancy were the major factors influencing TV.TSH and positive TGAb were the strongest risk factors of goiter.Impact of these factors mentioned above should be taken into consideration when TV and TGR were used to evaluate the iodine status.2.In the condition of iodine sufficient,TV may increases during pregnancy.Increase of BSA as a result of weight gain during pregnancy may be the most important reason.