Classification of maternal thyroid function in early pregnancy using repeated blood samples.

Area of Science:

• Reproductive Endocrinology
• Clinical Chemistry
• Obstetrics

Background:

• Maternal thyroid function assessment in early pregnancy requires careful consideration.
• Utilizing pregnancy-specific reference ranges is crucial for accurate thyroid hormone evaluation.
• The impact of serial blood sampling on thyroid function classification remains an area of investigation.

Purpose of the Study:

• To investigate whether repeated blood samples in early pregnancy influence the classification of maternal thyroid function.
• To determine the consistency of thyroid function status when assessed via serial blood draws.

Main Methods:

• A cohort of pregnant women with repeated early pregnancy blood samples was analyzed.
• Thyroid-stimulating hormone (TSH), free T4 (fT4), and thyroid antibodies (TPO-Ab, Tg-Ab) were measured.
• Classification of thyroid function utilized method- and pregnancy week-specific reference ranges.

Main Results:

• Thyroid function classification varied significantly between repeated blood samples in 1466 pregnancies.
• Approximately 49.4% of women with high TSH in the first sample also had high TSH in the second.
• Less than 20% of women with isolated fT4 changes in the first sample had similar classifications in the second sample.

Conclusions:

• Serial blood sampling can lead to considerable variation in classifying maternal thyroid function during early pregnancy.
• The agreement between repeated thyroid function tests depends on TSH levels and antibody presence.
• Clinical focus should be on the severity of thyroid function abnormalities in pregnant individuals.