Range Of Normal Value Of Thyroid Function Indexes In Pregnant Women In Cangzhou Area

Objective: To establish the thyroid-specific serum marker value range of the pregnant women in early pregnancy(T1, first 12 weeks), the second trimester(T2,13-27 th week), and late pregnancy(T3, 28 th week through delivery) in this area.To analyze the changes and relations of the TSH, FT3, FT4 in these three periods.Through the calculation of TPOAb,TGAb positive rate,to compare the prevalence of hypothyroidism in TPOAb positive serum and negative serum group.To compare the difference between the reference ranges of establishing in this study and the reference ranges proposed by American Thyroid Association and Chinese diagnosis and treatment guideline on thyroid disease in pregnancy and post partum 2012(Guideline).To compare the difference while screening hypothyroidism between the reference ranges of TSH, FT4 according to reference ranges of TSH, FT4 in Chinese Guideline 2012 and those established in this study among pregnant women.Method: 786 pregnant women who experienced the antenatal examination in Cangzhou people’s Hospital from August,2013 to December, 2014 were randomly selected as Group I to test their thyroid function. The chemiluminescence immunoassay was used to measure FT3, FT4, TSH, TPOA b and TGAb. Based on results obtained from Group I, 647 women was enrolled as Group II according to National Academy of Clinical Biochemistry(NACB) criteria. All the pregnant women were divided into T1, T2 and T3 groups according to their gestational weeks. Earlier than 12 weeks, T1, from 13 th week to 27 th week, T2,later than 28 th week until delivery, T3. Each group was composed of more than 120 subsjects. 174 non-pregnant women who were subjected to antenatal examination in this hospital were chosen as control group.The cross-sectional study method and 95% confidence interval were adopted to establish the specific serum marker value range in T1, T2 and T3 and analyze them respectively. Percentile statistic analysis was used to analyze the positive rate of TPOAb, TGAb in Group I. The TSH, FT4 reference ranges set in Group II was used to calculate the prevalence in Group I and compare the difference between the prevalence of positive TPOAb and negative serum. Screening difference between the two reference ranges was compared.Results:1 The TSH reference ranges of normal pregnant women in T1, T2, T3 are(0.18-3.87)m IU/L,(0.23-4.14)m IU/L,(0.59-5.72)m IU/L, respectively,FT4 are(12.18-22.35)pmol/L,(10.17-17.51)pmol/L,(8.86-16.72)pmol/L, respectively,FT3 are(3.32-6.01)pmol/L,(2.98-5.57)pmol/L,(2.84-5.01)pmol/L, respectively.2 The serum TSH and FT3 present negative correlation in pregnant women in their whole gestation period(P<0.01, r=-0.252). TSH and FT4 present negative correlation(P<0.01, r=-0.288). FT3 and FT4 present positive correlation(P<0.01, r=0.322).3 The positive rate of TPOAb in pregnant women was 10.80%, the positive rate of TGAb was5.80%.the positive TPOAb prevalence rate of clinical hypothyroidism, subclinical hypothyroidism and Low T4 are 2.35%, 4.71% and 4.71%, respectively.The negative TPOAb prevalence rate are 0.29%, 2.71% and 2.28%, respectively.4 According to the reference ranges of TSH, FT3, FT4 set by this research, the prevalence rate of hypothyroidism, subclinical hypothyroidism, Low T4 concentration are 0.51%, 2.93% and 2.54%, respectively. The results by according to the Guideline are 0.38%, 2.67% and 2.16%, respectively.Conclusions:1 Reference ranges of thyroid function for pregnant women in Canzhou area have been established.2 The reference ranges for T1, T2, and T3 pregnant women are above those recommended by ATA but below those by Chinese Guideline 2012.3 TSH for T1, T2 pregnant women is lower than non-pregnant women, especially over T1 phase, but then gradually increases, and till T3, the level is close to that of non-pregnant women. FT4 and FT3 is lower throughout pregnancy than those of non-pregnant women and presents a downtrend.4 The prevalence of hypothyroidism in those with TPOAb positive serum is higher than that in those with TPOAb negative serum, which indicates the correlation between positive TPOAb and hypothyroidism.5 There is difference in prevalence between screenings of hypothyroidism according to reference ranges of TSH, FT4 in Chinese Guideline and according to those established in this study among pregnant women, which demonstrates that the establishment of reference ranges of thyroid function for pregnant women in Canzhou area is important for early diagnosis of gestational thyroid diseases.