Trimester-specific reference intervals for thyroid function parameters in pregnant Caucasian women using Roche platforms: a prospective study

Abstract

Background: Standard thyroid function parameters reference intervals (RI) are unsuitable during pregnancy, potentially resulting in incongruous treatments that may cause adverse effects on pregnancy outcomes. We aimed at defining trimester-specific TSH, FT4 and FT3 RI, using samples longitudinally collected from healthy Caucasian women.

Materials and methods: Blood samples from 150 healthy Caucasian women, who had a physiological gestation and a healthy newborn at term, were collected in each trimester and at around six months post-partum. They showed mild iodine deficiency. After excluding women with overt TSH abnormalities (> 10 mU/L) and/or TPO antibodies, data from 139 pregnant women were analyzed by means of widely used Roche platforms, and TSH, FT4 and FT3 trimester-specific RI were calculated. Post-partum data were available for 55 subjects.

Results: Serum TSH RI were 0.34-3.81 mU/L in the first trimester, and changed slightly to 0.68-4.07 U/L and 0.63-4.00 mU/L in the second and third trimester, respectively. Conversely, both FT4 and FT3 concentrations progressively decreased during pregnancy, the median values in the third trimester being 14.8% and 13.2% lower, respectively, than in the first trimester. Thyroid function parameters in the first trimester were similar to those measured after the end of pregnancy.

Conclusions: This study calculates trimester-specific RI for thyroid function parameters in pregnancy, and proposes the reference limits that should be adopted when using Roche platforms in Caucasian women.

Keywords: FT3; FT4; Pregnancy; Reference interval; TSH; Thyroid function.

Fig. 1

Box and whisker plots of the TSH (A), FT4 (B) and FT3 (C) serum concentrations in the three trimesters of pregnancy and in the post-partum. In these plots, the horizontal lines inside each box represent the medians, while the box frames include the interquartile ranges (25–75 percentile). The vertical lines extend from the minimum to the maximum values excluding outside values, defined as values smaller than the lower quartile minus 1.5 times the interquartile range, or greater than the upper quartile plus 1.5 times the interquartile range, which are displayed as separate points. The paired results of each time point were compared by the Wilcoxon test. *P < 0.05–0.011; **P ≤ 0.010–0.001