Assessment of thyroid function during pregnancy: the advantage of self-sequential longitudinal reference intervals.

INTRODUCTION: To evaluate clinical value of a new self-sequential longitudinal reference intervals of thyroid function during pregnancy. MATERIAL AND METHODS: WE ESTABLISHED TWO DIFFERENT SERIES OF REFERENCE INTERVALS: self-sequential longitudinal reference intervals (SLRI) and general gestation-specific reference intervals (GSRI). For SLRI, the serum of 301 cases were collected five times in every case throughout the gestation. For GSRI, A total of 1455 subjects included in the study. We collected the serum respectively at various trimesters. We used TSH of both reference intervals to screen 1744 pregnant women, and compared the percentage of potential misclassification. RESULTS: Both SLRI and GSRI differed substantially from that for non-pregnant women (p < 0.05). There are similar fluctuations of serum TSH, FT4 and TPO-Ab during normal pregnancy. Although there were no significant differences in most reference intervals between SLRI and GSRI. But the IQR of SLRI were usually smaller than GSRI , especially in 1(st) trimester. Two hundred and fifty two women (14.4%) at various trimesters whose serum TSH concentration was within SLRI would be misclassified, while 23 women (1.3%) with a TSH concentration outside limit would not be identified. 0.11-3.84% women would got thyroid diseases during pregnancy. Subclinical hypothyroidism is most common maternal thyroid disorders. CONCLUSIONS: The SLRI can reflected the changes of thyroid function realistically, and can be used to decrease the percentage of potential misclassification of thyroid dysfunction during pregnancy. Screening for thyroid dysfunction of pregnant women is recommended and important.