The Reference Range Of Thyroid Hormones In Normal Pregnant Women And Related Research

Thyroid hormone is an important endocrine hormone involved in human metabolism,growth and development and multiple organ functional activities. Thyroid function status isof crucial importance for normal pregnancy and fetal development. Gestational thyroiddiseases increase the incidence of various complications, and may result in fetalmalformations, abnormal thyroid function, growth restriction, low birth weight and nervoussystem dysplasia. Low thyroid hormone levels during pregnancy may causeneurodevelopmental disorders, which are irreversible and significantly affect theintelligence level. Therefore, maternal thyroid function not only impact on the pregnancyitself,but also plays an important role in the development of their offspring. Normal thyroidhormones during pregnancy is an important condition to maintain the normal developmentof the offspring.During normal pregnancy, thyroid function is faced with complicated physiologicalchanges. These physiological changes all make gestational thyroid hormone level changesaccordingly. The thyroid hormone level is different between pregnant and non pregnantwomen due to the special gestational thyroid physiological changes.So if we determingestational thyroid function by the thyroid hormone reference values in healthy non pregnantpeople,the misdiagnosis and missed diagnosis rate of gestational thyroid diseaseswill increase, as well as the difficulties of clinical diagnosis and treatment of thyroiddisease during pregnancy. In July2012, the Chinese medical association endocrine branchand Perinatal medical branch jointly promulgated <the pregnancy and postpartum thyroiddisease diagnosis and treatment guideline>, pointing out that different areas, different races,different iodine intake status and special physiological metabolism during pregnancy canaffect the incidence rate of the thyroid diseases. The guideline suggests that every regionand hospital should set up their own specific reference ranges of serum thyroid functionduring pregnancy. At present only a few areas have established the specific referencevalues during pregnancy, and as one of the most populated province, there are no researchabout pregnancy-specific reference values in Henan Province. This research aim to detectserum thyroid hormone levels of healthy pregnant women in different pregnancy periods,study its change law, establish the region gestational thyroid hormone reference intervals,and reduce missed diagnosis and misdiagnosis of thyroid diseases during pregnancy. It hasclinical significance for early diagnosis and early intervention of gestational thyroiddiseases, and can maximize the reduction of adverse pregnancy outcomes for mother andchild.ObjectiveTo establish the trimester-specific reference ranges of thyroid hormone for normalpregnant women, and to study the change law to provide clinical evidence for earlydiagnosis and treatment of thyroid disease in pregnancy.Materials and Methods1Study populationThree thousand and eighty seven healthy pregnant women presenting to the third affiliated hospital of Zhengzhou University from September2013to december2013were included. Fivehundrand and eighty three antibody negative pregnant women were randomly selected as the studygroup, and were divided into three groups according to gestational ages. Meanwhile187healthy nonpregnant women were chosen as the control group. In which166people of serum TPOAb positive wereput into the TPOAb positive group.2Inclusion criteriaInclusion criteria were established according to the National Academy of Clinical Biochemistry(NABC) recommended standard, requiring no history of thyroid diseases and family history, nometabolic syndrome history and family history,medical history and family history, no palpable goiter,not taking thyroid medication and iodine-containing drugs, serum thyroid antibody negative, the growthof living in Zhengzhou, Han nationality and the usual consumption of iodized salt. For pregnant women,natural conception,no pregnancy complications and single birth were also required. All research subjectswere asked in detail about the general situation, pregnancy history, health status, diet, a history ofthyroid deseases and other medical history. Physical examination and a unified designed questionnairewere conducted.3MethodsAll entrants is collected blood5ml in the morning at empty stomach,the blood samples placedtwo hours for centrifugal extract serum. All serum detected thyrotropin, free thyroxine and thyroidperoxidase antibody by super-sensitive chemiluminescence immunoassay.4Statistical analysisSPSS17.0was used to analyze the data．Normal distribution data used independent sample t-test,Multiple group comparisons were made using Kruskal-wallis test. Groups were compared usingMann-Whitney test. Reference values of thyroid hormone function parameters using bilateral limit of 95%reference range, the results indicated by the median M and bilateral limits (P2.5and P97.5). a=0.05is the test standard.Results1Gestation age-specific reference intervals for TSHThe thyroid hormone levels between different pregnancy stages has stastistical signanficancecompared with non pregnancy groups (P<0.01). In the1st、2nd and3rd trimester pregnancy, the serumTSH reference values were respectively1.48(0.27~4.38) mIU/L,1.84(0.55~4.57)mIU/L and2.21(0.71~5.80) mIU/L. TSH concentration decreased significantly in the early pregnancy, and medianTSH decreased by34.80%compared with non-pregnant group (P <0.01), TSH thereafter graduallyincreased with gestational stages, and in the3rd trimester pregnancy, there was no statistical differencebetween pregnancy and non-pregnancy.2Gestation age-specific reference intervals for FT4In the1st、2nd and3rd trimester pregnancy, the serum FT4reference values wererespectively14.56(10.17~19.91)pmol/L.11.73(8.28~15.87)pmol/L and10.45(7.44~14.17) pmol/L. In the1st trimester serum FT4has no significant difference compared with non-pregnant group, and FT4leveldecreased in the2nd and3rd trimester, significantly lower than that in the non pregnancy group（P<0.01).In the2nd and3rd trimester serum FT4was28.86%lower than the median value of the non pregnancygroup.3Relation between TSH and TPOAb positiveIn pregnancy thyroid autoantibodies positive rate was7.48%, in which TPOAb positive rateaccounted for5.40%. Serum TSH values in TPOAb positive pregnancy in the1st、2nd and3rd trimesterwere significantly higher than TPOAb-negative women in pregnancy, the difference was statistically significant (P <0.05).Conclusion1. There are significant differences in the thyroid hormone levels between pregnancy and nonpregnancy, and significant differences also exist between different stages of pregnancy, thus to establishtrimester-specific reference values of thyroid hormones during normal pregnancy may be meaningful forclinical practice.2．In this study, the reference values of thyroid function in pregnant women specifically provide thebasis for Zhengzhou.