Reference Intervals For Common Thyroid Function Tests In Pregnant Women And Epidemiological Study On Thyroid Diseases In The Second Trimester Of Pregnancy

Objective: To establish the gestational-related reference intervals for thyroidfunction tests (TFT) in Chinese women,To investigate the incidence of thyroiddiseases in the second trimester of pregnancy and the effects on thyriod function inneonates.Methods: The study was surveyed in population taking their prenatal care at theclinic of the International Peace Maternity&Child Health Hospital affiliated toShanghai Jiaotong University School of Medicine.PARTⅠ:Serum samples werecollected from693normal pregnant Chinese women and divided into five groupsaccording to their gestational age:9-13,16-20,24-28,32-34and37-40weeks.Thyroid stimulating hormone (TSH) and free thyroxine (FT4) levels weredetermined by two different detection reagents: Abbott Architect I2000and RocheCobas Elecsys600. The reference ranges of the TFT indexes were calculatedaccording to the National Academy of Clinical Biochemistry (NACB). The2.5th and97.5th percentiles of each stage were calculated.PARTⅡ: A retrospective study wasconducted on1889pregnant women (13–27weeks) who were divided into high-riskand low-risk groups according to the backgrounds of them collected byquestionnaire. We detected the prevalence of thyroid dysfunction in high-risk groupsand low-risk pregnant women by normal reference range during the second trimesterin our research.Results: Thyroid hormone levels varied greatly among different gestationalstages. TSH levels measured by two different kits showed consistent changingpattern during pregnancy and displayed linear correlation (r=0.833-0.973,P<0.001).In9-13gestational weeks, TSH levels were significantly lower than that of other groups; and in37-40gestational weeks, it was higher than that of other groups(FAbbott=18.830, FRoche=21.012, all P <0.001). TSH reference ranges determinedby Roche detection reagent in each group were higher than those by Abbott detectionreagent (|t|=3.002,4.948,6.353,4.636and4.391, P <0.01, respectively). FT4levelswere higher in9-13gestational weeks than that of other groups (FAbbott=17.230,FRoche=14.439, P<0.001). FT4levels determined by Roche reagent were higherthan Abbott reagent in9-13weeks,(|t|=4.964, P<0.001), and lower in24-28and37-40weeks (|t|=4.183, P<0.001and|t|=2.417, P=0.016, respectively). The TSHlevel was correlated with FT4levels in9-13gestational weeks by detectionreagents (for Abbott reagent, r=-0.319for FT4P<0.001; for Roche reagent, r=-0.352for FT4, P<0.001).High-risk groups accounted for10.69%of all the pregnant women in this study.Using targeted high-risk case screening strategy, misdiagnosis rate of pregnancywith hyperthyroidism, subclinical hyperthyroidism, pregnancy with hypothyroidism,subclinical hypothyroidism, low T4syndrome and positive TPOAb were87.5%(14cases),87.08%(155cases),87.08%(155cases),83.93%(47cases),89.47%(17cases) and88.35%(91cases), respectively. Furthermore, there was no statisticallysignificant difference between high-risk group and low-risk group in the prevalenceof thyroid dysfunction.Between the1889pregnant women which in the second-trimester，56pregnantwomen with subclinical-hypothyroidism were detected，the detection rate was2.96%（56/1889）；19pregnant women with were detected，the detection rate was1.01%（19/1889）.If compared with the euthyroid group，the morbidity of the pregnancycomplications，like anemia，fetal distress，hypertensive disorder in pregnancy forthe subclinical-hypothyroidism group and hypothyroxine group showed nosignificant difference.The TSH level detected from the heel blood of neonate had nostatistical significant difference between the subclinical-hypothyroidism group andhypothyroxine group compared to the euthyroid group（χ2=0.552； P=0.759>0.05）.Conclusions: Accurate evaluation of TFT in pregnant women should be basedon the gestational-related reference intervals in Chinese population, and different detection reagents should also establish their own reference intervals.we believe thatuniversal screening to pregnant women can effectively reduce misdiagnosis rate ofthyroid dysfunction. Further, we recommend universal screening for thyroid functionin second trimester of pregnancy.Compared to the euthyroid pregnant women，themorbidity of anemia，fetal distress，hypertensive disorder in pregnancy for thesubclinical-hypothyroidism and hypothyroxine pregnant women showed nosignificant difference；Gestational subclinical-hypothyroidism showed no significantadverse effect on the thyroid function of neonate.