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Objective: To establish reference values of fetal thyroid glands from 200/7 weeks to 366/7 weeks of gestation
Materials and Methods: This was cross-sectional study to measure fetal thyroid gland parameters in 184 pregnant women at gestational age (GA) 200/7- 366/7 weeks that had no systemic diseases or history of thyroid disorder. The fetal thyroid circumference (FTC), fetal thyroid area (FTA) and fetal thyroid transverse diameter (FTTD) were ascertained by 2-Dimension (2D) ultrasound. The exclusion criteria were abnormal maternal thyrotropin stimulating hormone (TSH) levels, fetal abnormalities, inability to identify the fetal thyroid gland, and abnormal neonatal TSH levels/neonatal goiter. The parameters were calculated for the mean + SD and also plotted against gestational age. The nomograms were presented according to gestational age as percentiles. The expected value of each measurement was established using a linear regression formula. The Intraclass correlation coefficients (ICCs) had been used to evaluate the intraobserver and interobserver variations.
Results: Mean + SD of FTC, FTA, and FTTD were 3.78 + 0.68 cm, 1.12 + 0.38 cm2, and 1.36 + 0.29 cm, respectively. All parameters tended to increase with gestational age. According to the regression model, the expected FTC, FTA, and FTTD can be calculated using the following formulas: FTC (cm.) = 0.289642 + [0.1239246 x GA (weeks)](p<0.01), FTA (cm.2) = [0. 068565 x GA (weeks)] - 0.8160961(p<0.01), and FTTD (cm.) = [0.0490783 x GA (weeks)] - 0.0185486(p < 0.01). Intraobserver coefficients were 0.982, 0.977, and 0.935 for FTC, FTA, and FTTD. Interobserver coefficients were 0.989, 0.986, and 0.976 respectively. Nomograms for each gestational age were also created.
Conclusion: We established normal reference values for the thyroid glands of fetuses in Northeastern Thai women. These reference values may be helpful in monitoring for fetal thyroid disorder in fetuses determined to be at high risk for the condition and providing appropriate antenatal management
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