Second trimester fetal nasal bone length in a low-risk Turkish population.

Objective: To define normal values of second trimester fetal nasal bone length (NBL) in a low-risk Turkish population.

Method: Prenatal records of singleton fetuses who underwent second trimester ultrasonographic examination in the 16 to 23 weeks of pregnancy were retrospectively analyzed for NBL and biometric measurements (BPD, FL and HL). The relationship among NBL and gestational age (GA), biparietal diameter (BPD), femur length (FL) and humerus length (HL) was determined. Additionally, percentile values of NBL for each gestational week were provided.

Results: A total of 1467 fetuses were included in this study. There was a significant linear association among NBL and GA (R(2) = 0.709), BPD (R(2) = 0.752), FL (R(2) = 0.742) and HL (R(2) = 0.747). Fifth percentile values of fetal NBL were 3.11 mm for 16th, 3.50 mm for 17th, 3.70 mm for 18th, 4.10 mm for 19th, 4.50 mm for 20th, 4.62 mm for 21st, 5.24 mm for 22nd and 5.37 mm for 23rd gestational weeks.

Conclusion: The study provides normal ranges of NBL between 16 and 23 weeks of pregnancy in a low-risk Turkish population. Future studies with larger sample sizes including pregnancies carrying high risk for aneuploidy are needed to define cut-off values for NBL.