Objective To analyze the changes of thyroid function of healthy primipara before 20 weeks of gestation to establish normal gestational age-specific reference interval of thyroid hormones,and to investigate the prevalence of maternal thyroid disorders during the first half of pregnancy.Methods A total of 1605 healthy primipara without risk factors of thyroid diseases before 20 gestational weeks and 200 non-pregnant healthy women who accepted pre-conception care in Beijing Friendship Hospital from September 2010 to June 2011 were tested for serum thyroid stimulating hormone (TSH),free thyroxine (FT4) and thyroid peroxidase antihody (TPOAb) by chemiluminometric immunoanalysis.One thousand two hundred and fourty-three pregnant women among them with negative thyroid antibooly and without previons thyroid diseases were selected as the standard population for normal interval.Gestational age-specific percentile categories for TSH and FT4 were calculated.The prevalence of maternal thyroid disorders was examined by gestational agespecific intervals.Results (1) Compared with non-pregnant women,the median value of serum TSH in pregnant women decreased by 29.56％ to the value of 0.91 mU/L; while that of FT4 rose by 7.79％ to the value of 11.33 pmol/L before 12 weeks; and TSH increased while FT4 decreased during 13 to 20 weeks.(2) The median values and reference intervals (2.5th percentile,97.5th percentile) for TSH were 1.59 mU/L (0.15 mU/L,5.19 mU/L) in no-pregnant women,1.12 mU/L (0.03 mU/L,3.67 mU/L) at 8-12+6 gestational weeks,1.21 mU/L (0.05 mU/L,3.74 mU/L) at 13-16+6 gestational weeks,1.50 mU/L (0.31 mU/L,4.33 mU/L) at 17-19+6 gestational weeks; and the median values and reference intervals (2.5th percentile,97.5th percentile) for FT4 were 9.91 pmol/L (6.69 pmol/L,14.03 pmol/L),10.68 pmol/L (7.98 pmol/L,18.66 pmol/L),10.04 pmol/L (6.18 pmol/L,16.22 pmol/L),9.40 pmol/L (6.44 pmol/L,13.51 pmol/L) respectively.(3) According to gestational age-specific reference intervals,the general prevalence of maternal thyroid disorders,including hyperthyroidism,hypothyroidism,subclinical hypothyroidism and hypothyroinemia,was 3.55％ (57/1606).At 8-12+6 gestational weeks,13-16+6 gestational weeks and 17 19+6 gestational weeks,the occurrence of hyperthyroidism was 0.00％,0.13％ and 0.00％;that of hypothyroidism was 0.00％,0.13％ and 0.00％; the incidence of subclinical hypothyroidism was 3.60％,2.76％ and 3.00％; the occurrence of hypothyroxinemia was 0.16％,0.26％ and 0.86％,respectively.The positive rate of TPOAb at 8-12+6,13-16+6 and 17-19+6 gestational weeks were 22.91％ (140/611),16.56％ (126/761) and 15.45％(36/233),and the total positive rate of TPOAb was 18.82％ (302/1605).The median level of TPOAb was 38.90,41.87 and 39.10 mU/L,respectively.Conclusions Before 20 gestational weeks,specific changes occur in maternal thyroid function.TSH level decreases during 8 to 12 gestational weeks,and then increases gradually; while FT4 level increases during 8 to 12 weeks,and then decreases gradually.Thyroid dysfunction during pregnancy is common and subclinical hypothyroidisum is the leading problem in thyroid disorders.Screening for thyroid function during early pregnancy is suggested.

Objective To assess the prevalence of thyroid peroxidase autoantibody and relationships between thyroid function and TPOAb in the first trimester of pregnancy. Methods A total of 611 women during the first trimester from Beijing Friendship Hospital are tested for serum TSH,FT 4 and anti-TPO by chemilumino metric immunoanalysis . Women with previous thyroid diseases are excluded. We determine the reference intervals for TSH and FT 4 and establish the prevalence of TPOAb by using gestational age -specific interval. The relationships between TSH,FT 4 and TPOAb are analyzed. Results ( 1) The median value of TPOAb is 38. 9 mU / L,ranging from 6. 4 to more than1 300 mU / L at 8-12 gestational week . ( 2) The cutoff value of TPOAb is 206. 77 mU / L at the 90th percentile by using gestational age-specific interval. The positive rate of TPOAb is 10. 8% ( 66 /611) . ( 3) A simple regression analysis shows that serum titer of TPOAb correlates with the levels of TSH and FT 4 ( P = 0. 000 and 0. 000) . The median concentration of TSH is significantly greater in TPOAb-positive women than in TPOAb-negative women with increased value of 0. 40 mU / L. The risk of abnormally high TSH in former is more than three times than in latter. Conclusion TPOAb positive rate is 10. 8% in first trimester. Determination of the gestational age-specific intervals for TSH,FT 4 and TPOAb is of very importance to avoid overestimation of maternal thyroid dysfunction. Pregnant women with TPOAb-positive have a higher level of TSH and should be monitored closely for thyroid function.