Investigation of Bone Ratios for Prenatal Fetal Assessment in Taiwanese Population

The purpose of this study is to calculate the ratios of fetal limb bone to nasal bone length (NBL) obtained by transabdominal ultrasound between 19 and 28 weeks of gestation. Cross-sectional data were obtained from 1408 women with singleton pregnancies who underwent an advanced prenatal ultrasound examination from August 2006 to September 2008. The single measurement plane of fetal limb bones was on the longest section of each structure with appropriate image magnification. To assess repeatability of the intraobserver, two repeated measurements were obtained in 44 fetuses. The ratio of fetuses with biparietal diameter (BPD)/NBL was compared with those of fetal limb bones/NBL. The mean ratio was found between fetal NBL measurements and BPD (7.240), humerus length (HL) (4.807), radius length (RL) (4.157), ulna length (UL) (4.502), femur length (FL) (5.131), tibia length (TL) (4.528), and fibula length (FiL) (4.507). The reference ranges of fetal long bone length/NBL ratios for the second trimester was established by transabdominal sonography. There were no significant increases in these ratios with gestational age, especially the HL/NBL ratio.