Assessment of fetal gestational age in different trimesters from ultrasonographic measurements of various fetal biometric parameters

Introduction: Fetal biometry is a methodology devoted to measuring several parts of fetal anatomy and their growth. Aim: The present study was carried out to assess gestational age in the second and third trimesters with the help of ultrasonographic measurements of four fetal biometric parameters (i.e., biparietal diameter [BPD], head circumference [HC], abdominal circumference [AC], and femur length [FL]) in the local population (Jaipur Zone) of Rajasthan, and also to evaluate efficacy and significance of these four fetal biometric parameters in the prediction of gestational age by ultrasound. Materials and methods: Three hundred and thirty cases of normal pregnant females were studied (165 - second trimester [13-28 weeks] and 165 - third trimester [29-40 weeks]) with the known last menstrual period (LMP) and studied once during gestation. Results: Biparietal diameter and head circumference were found to be equally best predictors of gestational age and to determine the expected date of delivery (EDD) in the second trimester and BPD and FL in the third trimester. Abdominal circumference was the least accurate parameter in both trimesters. Variability in predicting gestational age (using all four parameters) was +/- 2 weeks in the second trimester and +2 to -4 weeks in the third trimester. The accuracy decreased and variability increased as the pregnancy advanced from the second to third trimester. Mean measurements of fetal biometric parameters were found lower than Western monograms in each week of both trimesters. Conclusions: Variation in predicted gestational age by ultrasonography (USG) is attributed to the anthropometric difference between the two populations due to racial, genetic, nutritional, and socioeconomic factors. Therefore, population-specific measurements should be made to generate tables and regression equations for more precise reporting of gestational age and EDD by USG. Copyright (C) 2013, The Anatomical Society of India. All rights reserved.