JCEM: TSH and FT4 Reference Intervals in Pregnancy

Background: Adequate thyroid hormone supply during pregnancy is important for an uncomplicated pregnancy and optimal fetal growth and developmen.

The latest addition to the ATA guidelines is the option to employ reference intervals calculated in centres with similar populations using the same detection method, which is a step between the gold standard and the fixed TSH upper limit approac.

Although methods using a fixed upper TSH limit compared to the gold standard may lead to considerable under- and over-diagnosis due to inter-population and inter-assay variability, methods for subtracting absolute numbers from non-pregnant reference intervals have not been thoroughly investigate.

Objectives: 1) To provide an overview of published reference intervals for TSH and FT4 in pregnancy; 2) to combine raw data from different cohorts to assess the consequences of common methodological differences between studie.

Methods: 1) Search Ovid MEDLINE, EMBASE, and Web of Science until December 12, 2021. Studies were evaluated in duplicat.

Figure 1 Study selection flow char.

Figure 2-3 * Reference interval calculated using data from individual participants in the consortium; ◯ iodine adequacy; ▽ mild to moderate iodine deficiency; △ iodine excess statu.

Figure 4 * Reference intervals calculated from individual participant data in the consortium; ◯ iodine adequacy; ▽ mild to moderate iodine deficienc.

Conclusions: We provide an overview of clinically relevant reference intervals for TSH and FT4 in pregnanc.

Original source: Osinga JAJ, Derakhshan A, Palomaki GE, et a.