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

OBJECTIVE

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

STUDY DESIGN

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).

RESULTS

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.

CONCLUSIONS

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.