Establishment Of Reference Value Of Specific Thyroid Function In Pregnant Women And Effects Of Gestational Isolated Hypothyroxinemia On Pregnancy Outcomes

Objective :The study was performed to calculate the reference intervals of thyroid hormones of the second and third timester women and expore the effects of isolated maternal hypothyroxinemia on pregnancy outcomes and neonatal comlications.Methods :A total of 269 healthy pregnant women with regular prenatal examination were recruited in the Second Affiliated Hospital of Guangxi Medical University from July 2018 to December 2020.Thyroid stimulating hormone(TSH),free thyroxine(FT4),free iodine thyroid glycine(FT3)and thyroid antibodies(TPOAb、Tg Ab)levels were examined.Based on the guideline issued by the National Academy Clinnical Biochemistry,the study established the reference value of thyroid function of the second and third timester women.In addition to,the study used the first trimester-specific normogram of thyroid hormones which had been established in our laboratory to define first trimester isolated maternal hypothyroxinemia.A total of 38 women with isolated hypothyroxinemia in the first timester of gestation were selectd as the case group,at the same time,45 women with normal thyroid function and TPOAb、Tg Ab negative in the first timester of gestation were randomly selected as the control group.The condition changes of the two groups were recorded during the whole gestational process.The adverse pregnancy outcomes between the two groups were compared.Results:The reference values of FT3 in the second and third timester women were 3.09-5.21 pmol/L,3.08-5.10 pmol/L,FT4 were 6.30-10.44 pmol/L,5.44-10.29 pmol/L,and TSH were 0.44-4.32 m IU/L,0.49-4.47 m IU/L,respectively.There were no significant differences in age,gestational age,number of productions and TSH level between the pregnant women in the case group and the control group.the FT4 level in the case group was significantly lower than that in the control group.Compared with the control group,the incidence of macrosomia and cesarean section in the case group were respectively 13.16%(5 cases)and 55.26%(21 cases),which were significantly higher than 0%(0 cases)and 31.11%(14 cases)in the control group(P<0.05),and no differences were observed between the two groups in terms of gestational hypertension,gestational diabetes mellitus,intrahepatic cholestasis during gestation,premature delivery,umbilical cord abnormality and fetal growth restriction(P>0.05).Conclusion:1.The reference values of thyroid function in the second and third trimester of pregnancy were successfully established in our hospital.2.The reference value of thyroid function is different between normal pregnant and non-pregnant women.FT3,FT4 and TSH change in different gestational period.Therefore,it is very necessary to establish the reference value of pregnancy-specific thyroid function.3.Pregnant women with isolated hypothyroxinemia in the first pregnancy are at increased risk of adverse pregnancy outcomes,especially for macrosomia and cesarean section.Levothyroxine therapy may be considered in isolated hypothyroxinemia detected in the first trimester.