Purpose: To examine the interobserver variability for fetal biometry parameters and to investigate whether this variability affects the second-trimester maternal serum screening test (STMSS) results. Materials and Methods: A total of 60 singleton pregnancies who were scheduled for STMSS were investigated. Two experienced sonographers performed all examinations at the same visit. The risk calculations of screening were performed according to the each operator's biometric measurements separately. Interobserver variability in measurements of fetal biometrics and the effect of this interobserver variability on the screening results were assessed. Results: interobserver reliability for biparietal diameter (BPD) and femur length (FL) were 0.904 and 0.888 (p < 0.001), respectively. interobserver reliability coefficients for trisomy 21, trisomy 13/18, and neural tube defect were 0.887, 0.999, and 0.920 (p < 0.0001), respectively. Conclusion: The present results demonstrate that the interobserver reliability and agreement of ultrasound measurements of fetal biometry in cases of routine prenatal screening are highly reliable.