Fetal thyroid in two-dimensional ultrasonography: nomograms according to gestational age and biparietal diameter

To establish fetal thyroid nomograms based on gestational age and biparietal diameter and to compare obtained results with previously published data.

A cross-sectional study of 241 healthy pregnant women at 14-38 week of gestation was undertaken. Exclusion criteria were: known maternal thyroid or systemic disease, unknown date of last menstrual period, multiple pregnancy and fetal malformations. Fetal thyroid diameter (FTD), circumference (FTC) and area (FTA) were measured by two-dimensional ultrasonography and plotted against gestational age (GA) and biparietal diameter (BPD).

FTD, FTC and FTA increased logarithmically to GA and BPD. Fetal thyroid measurements as a function of GA were expressed by logarithmic formulas: ln(FTD)=3.6025-23.0315/GA, ln(FTC)=4.6227-22.8003/GA, ln(FTA)=6.6303-45.0831/GA. The following logarithmic formulas were obtained for fetal thyroid measurements according to BPD: ln(FTD)=3.4068-45.4271/BPD, ln(FTC)=4.4271-44.8359/BPD, ln(FTA)=6.2390-88.4408/BPD. There were highly significant correlations between thyroid measurements and GA or BPD: r=0.87-0.90, p<0.00001.

We have established age-dependent and age-independent nomograms of fetal thyroid. These nomograms will enable prenatal diagnosis in fetuses at risk of thyroid disorders.