Background: Gestational TSH and FT4 reference intervals may differ according to assay method but the extent of variation is unclear and has not been systematically evaluated. We conducted a systematic review of published studies on TSH and FT4 reference intervals in pregnancy. Our aim was to quantify method-related differences in gestation reference intervals, across four commonly used assay methods, Abbott, Beckman, Roche, and Siemens.

Methods: We searched the literature for relevant studies, published between January 2000 and December 2020, in healthy pregnant women without thyroid antibodies or disease. For each study, we extracted trimester-specific reference intervals (2.5–97.5 percentiles) for TSH and FT4 as well as the manufacturer provided reference interval for the corresponding non-pregnant population.

Results: TSH reference intervals showed a wide range of study-to-study differences with upper limits ranging from 2.33 to 8.30 mU/L. FT4 lower limits ranged from 4.40–13.93 pmol/L, with consistently lower reference intervals observed with the Beckman method. Differences between non-pregnant and first trimester reference intervals were highly variable, and for most studies the TSH upper limit in the first trimester could not be predicted or extrapolated from non-pregnant values.

Conclusions: Our study confirms significant intra and inter-method disparities in gestational thyroid hormone reference intervals. The relationship between pregnant and non-pregnant values is inconsistent and does not support the existing practice in some laboratories of extrapolating gestation references from non-pregnant values. Laboratories should invest in deriving method-specific gestation reference intervals for their population.

背景：妊娠期 TSH 和 FT4 参考区间可能因检测方法而异，但变化程度尚不清楚，尚未进行系统评估。我们对已发表的关于妊娠期 TSH 和 FT4 参考区间的研究进行了系统回顾。我们的目标是量化四种常用检测方法（雅培、贝克曼、罗氏和西门子）中妊娠参考区间的方法相关差异。

方法：我们检索了相关研究的文献，这些研究发表于 2000 年 1 月至 2020 年 12 月期间，针对没有甲状腺抗体或疾病的健康孕妇。对于每项研究，我们提取了 TSH 和 FT4 的特定孕期参考区间（2.5-97.5 个百分位数）以及制造商提供的相应非妊娠人群的参考区间。

结果：TSH 参考区间显示出广泛的研究间差异，上限范围为 2.33 至 8.30 mU/L。FT4 下限范围从 4.40 到 13.93 pmol/L，用贝克曼方法观察到的参考区间始终较低。非妊娠和妊娠早期参考区间之间的差异是高度可变的，对于大多数研究，妊娠早期的 TSH 上限无法预测或从非妊娠值推断出来。

结论：我们的研究证实了妊娠甲状腺激素参考区间的显着方法内和方法间差异。妊娠值和非妊娠值之间的关系不一致，不支持某些实验室从非妊娠值推断妊娠参考值的现有做法。实验室应投资为其人群推导特定方法的妊娠参考区间。