To investigate the relationship between thyroid ultrasound parameters and thyroid function in pregnant women, and to find the best parameters.

From February 2017 to September 2017, 120 pregnant women were examined in the Maternal and Child Health Care Hospital of Zhoushan, they were divided into early trimester group (9~12 weeks, 40 cases), mid trimester group (16~24 weeks, 40 cases), late trimester group (32~36 week, 40 cases). Forty cases of non-pregnant with normal thyroid function women were selected as control group. The diameters and resistance index (RI), end diastolic blood flow velocity (PDV) and peak systolic velocity (PSV) of each group were measured by ultrasound. The levels of thyroid stimulating hormone (TSH), free tri-iodothyronine (FT3) and free thyroxine (FT4) were detected by automatic biochemical analyzer.

There were no significant differences in the longitudinal thyroid diameter, transverse diameter, anteroposterior diameter, RI and PDV among the four groups (P>0.05). The PSV in the control group was significantly higher than that of the other three groups (F=7.224, P<0.05). The PSV in late trimester group was (28.03±8.10) cm/s, which was significantly lower than that in early trimester group (34.52±8.03) cm/s (t=3.599, P<0.01). The TSH in the early trimester group and the mid trimester group was significantly lower than that in the late trimester group and the control group (all P<0.05), and the early trimester group was the lowest, 1.09 (0.24, 3.20) mU/L. The FT3 and FT4 levels in the control group were significantly higher than that of the other three groups (all P<0.05). FT3 and FT4 levels in the late trimester group were 4.10 (3.61, 4.55) pmol/L and 12.20 (8.73, 15.01) pmol/L, respectively, which were significantly lower than those in the early trimester group and the mid trimester group (all P<0.05). There was a negative correlation between PSV and TSH in pregnant women (r_s=-0.334, P<0.05), and positively correlated with FT3 and FT4 (r_s=0.364, 0.377, both P<0.05).

The blood flow parameters PSV of superior thyroid artery in pregnant women is significantly higher than those in non-pregnant women, which is related to thyroid hormone (TSH, FT3 and FT4). Dynamic assessment of PSV in pregnant women is of great significance for evaluating thyroid function assessment in pregnant women.