Table 1.

The observed trimester‐specific reference intervals for TSH and FT4

Trimester	n	P2.5	95% CI (P2.5)	P97.5	95% CI (P97.5)
TSH, mlU/L
1st	188	0.59	0.52‐0.65	3.54	3.03‐3.79
2nd	133	0.80	0.71‐0.89	4.46	4.08‐5.00
3rd	157	0.72	0.44‐0.90	4.19	3.97‐4.87
FT4, pmol/L
1st	188	11.8	11.7‐12.2	18.4	17.4‐19.1
2nd	133	11.6	11.2‐11.8	17.4	16.3‐18.3
3rd	157	9.7	9.4‐10.1	15.1	14.6‐15.5

RI: reference interval; P2.5/P97.5: percentile 2.5%/97.5%; CI: confidence interval.