The human fetal thyroid I. Its weight in relation to body weight, crown‐rump length, foot length and estimated gestation age

The weights of 75 human fetal thyroids were analyzed in relation to crown‐rump length, foot length, weight, and estimated gestation age. The ratio of thyroid weight to body weight was lower in the smaller fetuses and gradually increased until the fetus was 70–90 mm in crown‐rump length when the ratio attained a value close to that found in the newborn and adult. This period of development when the relative weight of the thyroid becomes constant coincides with the time of appearance of colloid and the onset of ability to concentrate iodine. A comparison of estimated age of fetuses in the Danish material and the formalin‐fixed fetuses from the Carnegie Collection shows the Danish fetuses under 40 mm in crown‐rump length to be four to six days older than the average given by Streeter. Streeter may have made his average too low and probably the relative ages of the two groups are comparable.