The development of the foetal thyroid: in utero ultrasonographic measurements

The early recognition of potentially treatable thyroid disease in the foetus frequently depends on the detection of abnormal growth of the foetal thyroid gland. We have therefore established nomograms for foetal thyroid transverse width and circumference from 14 weeks of gestation until term, using transvaginal and transabdominal high-resolution ultrasound techniques.

A prospective, cross-sectional study of 193 normal singleton pregnancies was performed.

Thyroid size was measured by transvaginal ultrasonography between 14 and 17 weeks, and by abdominal ultrasound from 18 to 37 weeks of gestation.

Data was accurately obtained for 193 foetuses. The mean +/- SD thyroid width and circumference were 11.7 +/- 4.1 mm (95% confidence interval 11.1-12.3) and 39.5 +/- 14.1 mm (95% confidence interval 37.4-41.6), respectively. Thyroid size as a function of gestational age was expressed by the regression equations: thyroid width (mm) = -3.94 + 0.68 x gestational age (weeks), and thyroid circumference (mm) = -1.38 + 0.23 x gestational age (weeks). The correlation coefficients, r = 0.91 and r = 0.93, for thyroid width and circumference, respectively, were found to be highly statistically significant (p < 0.0001). The normal mean of thyroid width and circumference for each week of gestational age and the 95% prediction limits were defined.

The present data offer normative measurements of the foetal thyroid that may facilitate the prenatal diagnosis of foetal goitre and make early administration of in utero treatment possible.