THE DEVELOPMENT OF THE FETAL THYROID - IN-UTERO ULTRASONOGRAPHIC MEASUREMENTS

OBJECTIVE The early recognition of potentially treatable thyroid disea se in the foetus frequently depends on the detection of abnormal growt h of the foetal thyroid gland, We have therefore established nomograms for foetal thyroid transverse width and circumference from 14 weeks o f gestation until term, using transvaginal and transabdominal high-res olution ultrasound techniques. DESIGN A prospective, cross-sectional s tudy of 193 normal singleton pregnancies was performed, MEASUREMENTS T hyroid size was measured by transvaginal ultrasonography between 14 an d 17 weeks, and by abdominal ultrasound from 18 to 37 weeks of gestati on. RESULTS Data was accurately obtained for 193 foetuses, The mean +/ - SD thyroid width and circumference were 11.7 +/- 4.1 mm (95% confide nce 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 ag e was expressed by the regression equations: thyroid width (mm) = -3.9 4 + 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, respectivel y, were found to be highly statistically significant (P < 0.0001). The normal mean of thyroid width and circumference for each week of gesta tional age and the 95% prediction limits were defined, CONCLUSIONS 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.