Purpose: To investigate the correlation between fetal clavicle length and gestational age in pregnant patients from 14 and 27 weeks of gestation. Methods: This was a retrospective cross-sectional study of patients from 14 and 27 weeks of gestation. Ultrasonographic measurements such as abdominal circumference (AC), femur length (FL), humerus length (HL), clavicle length (CL), head circumference (HC), biparietal diameter (BPD), estimated fetal weight (EFW), and transverse cerebellum diameter (TCD) were made and compared. Results: A total of 552 patients were evaluated in our clinic and CL was measured properly and successfully in all fetuses. Fetal AC, FL, HL, CL, BPD, HC, EFW and TCD measurements were significantly and strongly correlated with gestational week, and Pearson’s correlation values were 0.964, 0.965, 0.959, 0.965, 0.951, 0.917, 0.925, and 0.954, respectively (p < 0.001). In the regression analysis equation, gestational week = 0.894 + CL × 0.961. Conclusion: There was a significant positive correlation between fetal CL (mm) and gestational week. We suggest that the 1 mm = 1 week rule can be used for patients with anomalies of the cerebellum and vermis, as well as for patients with unknown last menstrual period.