Assessment of Gestational Age in Second and Third Trimester by Occipto-frontal Diameter using Ultrasound

Abstract

The objective of this study was to estimate the gestational age using the occipitofrontal diameter in the second and third trimester using the known last minstrel period as a reference in estimating the accurate GA. The study was conducted at Alsouady hospital / Turkish teaching hospital on October 2016-December, 2016 by using ultrasound machine with convex transducer with variable frequencies ranging from (3-4 MHz).electronic caliper system set at a velocity of 1540m/s. This is a descriptive and analytical study of a cross sectional type with prospective data collection. The data of this study werecollected from 50 uncomplicated pregnant women between 14 and 40 weeks of gestation who presented for routine ultrasound. Only singleton pregnancies were included. Pregnant women with concomitant disease possibly affecting fetal growth (e.g. diabetes mellitus, asthma, hypertension, renal disease, thyroid disease) were not included as were those with complications of pregnancy. The results of this study showed that the mean value of the OFD was 81.1±24.6 mm which is the long axis of the head diameter versus the shorter diameter (BPD) was 63.7±20.2 mm with cephalic index (CI) of 0.81±0.1, the average GA using FOD was 26.5±7.3 weeks versus 26.5±7.7 weeks using LMP. There is no significant difference between the LMP calculation of GA and GA estimated using OFD. The result also showed that GA increases by 0.3 weeks/mm of OFD. In conclusion OFD can be used to estimate the GA with an accuracy > 92% in i.e. the OFD can explain more than 92% of the changes occur in the GA. Finally, the study showed the OFD can be used safely to predict the GA, but consideration of cephalic index is important to avoid over or under estimation of GA. The OFD mainly had exponential relationship with the GA rather than the linear trend although both trend gives insignificant difference from the LMP-GA.