Thyroid function and pregnancy – reference limits for TSH and fT4 in the first and second trimester of pregnancy
General Medicine, 2024, 26(6), 16-22.
B. Delev1,2, S. Stoencheva1,2
1Department of Clinical Laboratory, Faculty of Medicine, Medical University ‒ Plovdiv
2 UMHAT „Sv. George“ ‒ Plovdiv
Abstract. The periods, during which thyroid diseases most often occur, are associated with a specific hormonal readjustment of the body ‒ puberty, pregnancy, childbirth, breastfeeding and menopause. Of all of them, pregnancy is the highest risk period for overt or hidden manifestation of various thyroid pathology. Pregnancy deepens thyroid abnormalities, which can also affect the development of the future newborn. That is why, the recommendations of leading endocrine organizations such as the American Thyroid Association and the European Thyroid Association indicate that the optimal approach for assessing gestational thyroid function includes determination and application of trimester-specific values of indicators for each individual center, considering the features of the local population. The aim of the study is to develop population-specific reference limits for TSH and fT4 for the first and second trimester of pregnancy. Materials and Methods: Pregnant women over 18 years of age have been monitored for the development of the reference limits. Serum concentrations of TSH and fT4 were determined by chemiluminescence immunoassay using an automatic system (Access 2, Beckman Coulter). A parametric method is applied to determine the boundaries of the reference intervals. Data analysis was performed using IBM SPSS 26 and REFVAL 4,11. Results: Our results indicate that the reference intervals for TSH and fT4 in the first and second trimester are different from the intervals accepted for the non-pregnant population. In conclusion, the data from our study can be a reliable tool for the prevention, diagnosis, treatment and monitoring of thyroid disorders during pregnancy.
Key words: pregnancy, TSH, fT4, reference interval, thyroid dysfunction