Determination of Gestational Age by Fetal Tibial Length Using Ultrasonogrophy in Sudanese Pregnant Ladies

Abstract

Ultrasound has been used for assessment of the gestational age of the fetus for years. Tibial length is not used as routine in assessing the gestational age in many countries. The main objective of this study was to determine the gestational age by ultrasound measurement of tibial length of the fetus in the second and third trimesters of pregnancy. The study was conducted as facility-based descriptive cross sectional study conducted at alsaudi hospital,s antenatal care clinics. A total of 75 pregnant ladies in their second and third trimesters were enrolled to ultrasound measurements of the tibial length and also biparietal diameter and femur length during a period of two months. It was possible to obtain certain last menstrual period for all participants to assess the gestational age. A written informed consent was taken from all participants. In the manual assessment of gestational age from one to three days were omitted and from four to six days were considered a week. The tibial lengths at different gestational ages were measured in millimeters. The obtained tibial lengths were compared to standard reference values for same gestational ages. The gestational ages by certain last menstrual period was compared to that obtained from measured tibial length (R2 = 0.9428), femur length (R² = 0.953) and biparietal diameter (R² = 0.875). Analysis was done using T-test -to compare means- and other test for correlation. It was found that the mean gestational age by last menstrual period was statistically not significant (p<.829) when compared to mean gestational age by tibial length. At other hand the mean gestational age by last menstrual period was statistically significant (p<.000) when compared to mean gestational age by femur length and biparietal diameter. The mean gestational age by obtained tibial length was found statistically not significant (p<.120) when compared to mean gestational age by standard tibial length. Also the mean tibial length of obtained values was found statistically not significant (p<.709) when compared to mean tibial length of the standard values. Equation was obtained to calculate the gestational age using fetal tibial length which was; (GA= 0.4492 * TL + 8.2956). The study concluded that ultrasound fetal tibial length was good and more reliable in assessment of the gestational age in the second and third trimesters of pregnancy compared to femur length and biparietal diameter. But it needs a standard reference values for comparison. Negligible difference was found between obtained mean tibial length and mean tibial length of standard reference (R² = 0.951). Also a Negligible difference was found between gestational age of obtained tibial length and gestational age of standard reference (R² = 0.965). Using the above equation gestational age can be determined by ultrasound measurements of fetal tibial length. As pregnancy continues the femur length and biparietal diameter become less reliable in assessing gestational age compared to tibial length. Sudanese reference values for ultrasound fetal tibial length can be achieved using more reliable and well designed studies. Difficulty was found when measuring tibial length in early mid trimester of pregnancy.