Factors affecting the accuracy of the forecast fetal weight obtained by ultrasonographic measurements

Objective: Determination of the estimated fetal weight by evaluating the fetus by ultrasonography has become a routine of obstetric practice. . It has become one of the key clinical assessments to assess fetal growth and to decide on birth management. In addition, fundus-pubis measurement is also used clinically to estimate fetal weight. Although the fetal weight prediction is a cheap and easily accessible and feasible method with the measurement of fundus-pubis, an accuracy rate between 60-75% has been reported in the estimation of the actual birth weight. Estimating fetal weight is of great importance in order to predict macrosomia and intrauterine growth retardation and follow up fetal growth. The aim of this study is to compare the estimated fetal weight obtained by ultrasonographic and fundus-pubis measurements in the last trimester of pregnancy with birth weight and to reveal their accuracy, It is also an assessment of the factors affecting the estimated fetal weight. Material and Method: The study was designed prospectively and cross-sectionally. 500 pregnant women aged 34 weeks and over were included in the study between 06/02 / 2019-06 / 12/2019, who were hospitalized in Tokat Gaziosmanpaşa University Gynecology and Obstetrics Clinic for delivery. Pregnant women with intrauterine death, presence of congenital anomaly, amniotic membrane rupture, and multiple pregnancy were excluded. Pregnant women who did not have a pregnancy complication in the last trimester and delivered within one week after hospitalization were included in the study. Then, using the uterine fundus height and LOGIQ 3 device, the ultrasonographic fetal abdomen circumference (AC), biparietal diameter (BPD) and femur length (FL) were measured and the estimated fetal weight was calculated automatically with the hadlock formula registered in the device. Fetal weight estimation was made according to the Johnson formula with the data obtained by fundus-pubis measurement. The actual weight of the fetus after birth was recorded. All data were analyzed with Statistical Package for Social Sciences version 20 program. While analyzing the data, statistical significance was accepted as p <0.05. Findings: A total of 517 patients were included in the study. The birth weight values calculated according to the Johnson formula and USG were 3317.06 ± 602.17 and 3179.32 ± 465.62, respectively. Considering the estimated birth weights calculated according to the Johnson formula, a total of 232 values (44.9%) showed a deviation of ± 10% compared to the birth weight. Similarly, when the estimated birth weights calculated according to USG were examined, a total of 378 values (73.1%) deviated by ± 10% from birth weight. The number of babies born under 2500 grams was 38, the number of babies born between 2500-4000 grams was 452, and the number of babies born above 4000 grams was 27. Sensitivity 85.2% for the circumference of the abdominal circumference measured by prenatal USG in terms of macrosomic babies; specificity 80.2%; positive predictive value was 19.1% and negative predictive value was 98.9%. In addition, for babies born macrosomically, the sensitivity of the prenatal fundus pubis distance to the cm value of 38 cm was 62.9%; specificity 87.3%; positive predictive value was 21.5% and negative predictive value was 99.5%. In the fetuses with birth weight (TAD) below the estimated, the average amnion fluid index was found 12.08 with a deviation of 3.73, and 10.85 with 3.7 deviations in the fetuses with a birth weight (TÜD) above the estimated. In terms of fetal presentation, the head-to-head ratio was 90.2% in TAD and 96.2% in TÜD. When the placenta location was examined, fetuses with anterior location were 31.1% in TAD, other placental localizations were 68.9%, anterior placental location was 38% in fetuses with TUD, and other localizations were 62%. In the evaluation made according to fetal gender, 60.7% of female fetuses and 39.3% of male fetuses were below the estimated weight. It was determined that 34.2% of female fetuses and 65.8% of male fetuses are over the estimated weight. Result: The accuracy rates of Jhonsan formula and ultrasonography in detecting macrosomia were 63%, 29.6%, respectively. The accuracy rates of Jhonsan formula and ultrasonography in estimating fetal weight between 2500-4000g were 77% and 95.6%, respectively. It has been revealed that using non-ultrasonographic traditional parameters together with ultrasonography data, such as fundus pubis distance, positively affects the correlation. In the fetuses included in the study, there was no statistically significant difference in terms of placenta placement, fetus presentation and amniotic fluid index. In the evaluation made according to fetal gender, 60.7% of female fetuses and 39.3% of male fetuses were below the estimated weight. It was determined that 34.2% of female fetuses and 65.8% of male fetuses are over the estimated weight. The Johnson formula was found to be an effective method in fetal weight estimates. We think that fetal weight estimation can be made with the Johnson formula and will provide an advantage to the physician, especially in centers where there is no costly device such as ultrasonography. We believe that larger series of studies are needed in this regard. Keywords: Estimated fetal weight, pregnancy, ultrasonography, macrosomia, intrauterine growth retardation