Background: The determination of gestational age has a critical role in clinical practice on a daily basis for optimal neonatal management. Measurement of the transverse diameter of fetal thymus (TL) can be utilized for estimating the gestational age (GA).   Objective: to determine the accuracy of TL in estimation of GA of the fetus and to correlate TL with conventional fetal parameters viz. head circumference (HC), bi-parietal diameter (BPD), abdominal circumference (AC), femur length (FL) and with the GA, also, to detect linear regression formulae for estimation of the GA from TL and the other conventional fetal parameters. Methodology: This hospital based cross-sectional research was carried out on 282 pregnant women visited the outpatient obstetric clinic at Al-zahraa University hospital, from July to December 2022. Women with Singleton viable apparently normal fetus, GA between 17- 39 weeks were chosen to conduct the study. TL and the other conventional fetal parameters viz. BPD, HC, AC and FL were measured by ultrasound.   Results: There was an increase in the length of TL in relation to the increase of GA in weeks. There was a highly significant correlation (r) between the conventional fetal parameters viz. BPD, HC, AC, FL and TL also between the TL and GA. The linear regression formulae of TL and the other conventional fetal parameters had a statistically significant effect on estimating of the gestational age. Conclusion: There was a highly positive correlation between TL, the conventional fetal parameters viz. BPD, HC, AC, FL and GA. The TL gland can be used for estimation of GA.