OBJECTIVE: To determine sonographically the transverse diameter of the fetal thymus and present nomogram for the transverse diameter of the fetal thymus in uncomplicated singleton pregnancies between 19 and 38 weeks of gestation. SETTING: Department of Obstetrics and Gynecology, Charles University in Prague, Faculty of Medicine Hradec Kralove, University Hospital Hradec Kralove, Czech Republic. METHODS: A prospective study was performed. The transverse diameter of the fetal thymus was measured by the one experienced examiner in 198 healthy fetuses between 19 and 38 weeks of gestation. RESULTS: The transverse diameters of the fetal thymus were obtained from 183 of the 198 subjects. The regression equation was expressed as a function of gestational age: the transverse diameter of the fetal thymus (mm) = 1.001 × gestational age (week) - 0.932 or 0.143 × day - 1.34. Both the correlation coefficients, r=0.91 for weeks and r=0.92 for days were found to be highly statistically significant (p<0.0001). CONCLUSION: This study presents normative data (mean, 5th and 95th) for the ultrasound measurements of the transverse diameter of the fetal thymus in healthy singleton pregnancies.

Department of Obstetrics and Gynaecology Charles University Prague Czech Republic