Assessment of Fetal Nasal Bone Length and Nasofrontal Angle in the Second Trimester in Normal Indian Pregnancies

Abstract

The authors aimed to establish the reference ranges of fetal nasal bone length (NBL) in the second trimester and evaluate the relationship between fetal NBL and biparietal diameter (BPD) at 17–22 weeks of gestation in the Indian population. The authors also determined the normal ranges of the fetal nasofrontal angle (NFA). Ultrasound examination was done in 486 singleton pregnancies at 17–22 weeks of gestation. The fetal NBL was measured in millimeters in a strict sagittal view of the fetal head. The NFA was also measured in this mid-sagittal profile. The authors present the normal range of fetal NBL. Mean NBL was found to increase linearly with advancing gestation and BPD. The NBL appears to be marginally longer in Indian fetuses than other Asian fetuses. The minimum, maximum, and mean NFA values were 112, 142, and 130 degrees. The authors present the normal range of NBL in the second trimester in the Indian population and identify its linear relationship with gestational age. The normal range varies among races and so a relative percentile is a more reliable screening criterion than an absolute value. The authors present the normal ranges of fetal NFA from 18 to 21 weeks.