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Erschienen in:
31.07.2020 | Original Article–Obstetrics & Gynecology
Ultrasonographic assessment of fetal thyroid in Japan: thyroid circumference and distal femoral and proximal tibial ossification
Erschienen in: Journal of Medical Ultrasonics | Ausgabe 4/2020
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Purpose
The present study established a nomogram of fetal thyroid circumference (FTC) and the appearance timing of fetal distal femoral and proximal tibial ossification to assess fetal thyroid function in Japan.
Methods
Between April 2015 and July 2019, normal pregnant women at our hospital were recruited for the study. FTC was measured by the automatic ellipse outline and plotted against gestational age (GA). Fetal distal femoral and proximal tibial ossification measurements were obtained with standard electronic calipers from outer-to-outer margins (> 1 mm as the presence of ossification).
Results
A total of 199 pregnant women were examined. FTC increased logarithmically to GA. A nomogram of FTC was expressed by a logarithmic formula: \({\ln}\left( {{\text{FTC}}} \right)\, = \,{\exp}\left( {{4}.{679}0{-}{3}0.{3961}/{\text{GA}}} \right)\). The respective 5–95th percentiles of FTC at each GA were 20.2–36.2 mm at 22 weeks, 25.0–44.8 mm at 26 weeks, 29.2–52.3 mm at 30 weeks, and 32.9–59.0 mm at 34 weeks. The fetal distal femoral epiphysis was not visualized before 30 weeks, but was visualized in 100% of fetuses after 35 weeks of gestation. The fetal proximal tibial epiphysis was not visualized before 33 weeks, but was visualized in 73.7% of fetuses at 37 weeks of gestation.
Conclusion
We generated a GA-dependent FTC nomogram for Japanese fetuses. We also confirmed the appearance timing of fetal distal femoral and proximal tibial ossification to assess bone maturation. These assessments may be very useful for evaluating fetal thyroid function in Japan.