Normal ranges for fetal femur and humerus diaphysis length during the second trimester in an Iranian population.

Objectives: Shortening of the fetal long bones is a sonographic soft marker for screening of Down syndrome in the second trimester that can be influenced by ethnicity. The purpose of this study was to provide normal reference ranges for femur and humerus diaphysis length during the second trimester of pregnancy in an Iranian population.

Methods: This cross-sectional study was performed on 3011 singleton fetuses at 15 to 28 weeks' menstrual age. The relationship between menstrual age and both femur and humerus diaphysis length was determined, and percentile values for each menstrual week were provided.

Results: The median femur diaphysis length ranged from 18.05 mm at 15 menstrual weeks to 52.20 mm at 28 menstrual weeks, and the mean humerus diaphysis length ranged from 17.65 mm at 15 menstrual weeks to 48.10 mm at 28 menstrual weeks. There was a linear relationship between menstrual age and both femur diaphysis length (R² = 0.957) and humerus diaphysis length (R² = 0.941).

Conclusions: We have provided normal reference ranges for femur and humerus diaphysis length during the second trimester of pregnancy in an Iranian population.