Study on the levels of TSH and FT4 in different gestational weeks of normal pregnancy

ObjectiveTo explore the reference value of serum thyroid stimulating hormone(TSH) and free thyroxine(FT4) levels in different gestational weeks of normal pregnancy.

MethodsA total of 1 901 pregnant women with screening thyroid during pregnancy were retrospectively analyzed, and divided into the first trimester(T1, ≤11⁺⁶ weeks), second trimester(T2, 12-27⁺⁶ weeks) and third trimester(T3, ≥28 weeks) according to the gestational age at the time of detection.According to the specific gestational weeks, the puerpera were divided into the 0-11⁺⁶ weeks gestation group, 12-19⁺⁶ weeks gestation group, 20-27⁺⁶ weeks gestation group, 28~35⁺⁶ weeks gestation group and ≥36 weeks gestation group.The serological reference range of thyroid function indexes in different gestational weeks and periods of pregnancy were established.

ResultsThe differences of the levels of TSH and FT4 among different stages of pregnancy were statistically significant(P < 0.01), the TSH in T3 stage was (2.12±1.32) μU/mL, which was significantly higher than that in T1 and T2 stages(1.78±1.01)μU/mL and (1.83±0.95)μU/mL (P < 0.01).The upper limits of TSH reference range were 3.76, 3.79 and 4.71 μU/mL in T1, T2 and T3 stages, respectively.The FT4 of T3 stage was (0.52±0.09)ng/dL, which was significantly lower than that of T1 and T2 stages(0.84±0.18)ng/dL and (0.60±0.10ng/dL(P < 0.01).The FT4 of T2 stage was also significantly lower than that of T1 (P < 0.01).The differences of the TSH and FT4 levels among different gestational weeks were statistically significant(P < 0.01).The TSH level was the lowest at 12-19⁺⁶ weeks of gestation(P < 0.05), then increased with the increase of gestational age(P < 0.05), and the TSH level was the highest at ≥36 weeks of gestation(P < 0.05).The level of FT4 was the highest at 0-11⁺⁶ weeks of gestation(P < 0.05), lower than that at 0-11⁺⁶ weeks of gestation(P < 0.05), and tended to be stable with the increase of gestational age(P>0.05).

ConclusionsThe reference ranges of TSH and FT4 are different in different stages of pregnancy.The establishment of gestational age specific and method specific reference values in different stages of pregnancy and specific gestational age is helpful to guide the screening and management of thyroid diseases during pregnancy.