Trimester-specific thyroid hormone changes in normal pregnant Egyptian women

Abstract

Introduction The range of normal thyroid functions during pregnancy differs between ethnic groups. Establishment of trimester- and assay-specific reference intervals for every population is recommended. Aim Assessement of the changes in thyroid function tests across the different trimesters in normal pregnant Egyptian females. Subjects and methods The study included 150 normal pregnant Egyptian females, recruited from Cairo university hospital antenatal care clinic, with 100 age-matched non-pregnant females, as a control group. Serum thyroid stimulating hormone (TSH) and free thyroxine (FT4) were measured in the three trimesters of pregnancy for every patient. Thyroid peroxidase antibodies (TPO Abs) were also assessed. Our study showed that TSH reference ranges, using the 2.5th and the 97th percentiles, were 0.6–4.3, 0.9-3.7 and 1.0–4.2 mIU/ml for the first, second and third trimesters respectively. The median TSH concentration (50th percentile) was lower in the first trimester (2.1 mIU/ml) in comparison with the second and third trimesters of (2.6 and 2.9 mIU/ml respectively). FT4 reference ranges, using 2.5th to 97th percentile, were 0.9–2 and 0.7–1.4 and 0.6–1.2 ng/dl for the first, second and third trimesters respectively. The median FT4 concentration was higher in the first trimester (1.5 ng/dl) in comparison with the second and third trimesters of (1.1 and 1.0 ng/dl respectively). The percentage of positive TPO Ab was higher in pregnant women than that of age matched non-pregnant ladies (15.3 vs 2%, P<0.001). Conclusion Our study established trimester-specific changes in thyroid hormone reference ranges in normal pregnant Egyptian females. A larger population-based study would help to confirm those ranges.

Keywords

• pregnancy
• thyroid functions
• thyroid peroxidase antibodies
• thyroid-stimulating hormone