Analysis of factors influencing ultrasound-based fetal weight estimation

Determining the mean deviation between estimated fetal weight (EFW) measured by ultrasound biometry and the real final birth weight and defining the factors influencing the accuracy of weight estimation.

Estimated weight of the fetus before birth is valuable information for obstetricians particularlyin choosing the method, management, and timing of delivery.

The retrospective study analyzed 331 medical records of induced labor between January and June 2021. Fetal weight estimation was calculated using Hadlock formulas. The anamnestic data were obtained from medical records, namely: maternal age, maternal BMI, parity, date of the last ultrasonography (USG) before delivery, fetal presentation, placental location, EFW (including the physician's name performing the measurement, and time of the measurement), gestational age of the fetus, date of birth, fetal gender, neonatal weight and length. The correlations between the weight deviation and other factors were expressed using the Pearson and Phik (Φk) correlation coefficients. The Bland Altman method was used to visualize the correspondence between the two variables. The hypotheses were based on the acquired knowledge and then tested by Mann-Whitney U, Kruskal-Wallis, and ANOVA statistical tests, as required by the hypotheses and input data.

The mean EFW in the studied group was 3,459 ± 435 g, and the mean actual birth weight was 3,508 ± 508 g. The mean absolute deviation between monitored weight parameters was 260.27 g. The mean real birth weight was higher compared to EFW by 4.873 g. A significant effect on EFW was observed for the following factors: time interval between sonographic weight estimation and delivery (less than 7 days), high maternal BMI (> 30 kg/m2), maternal age, and neonatal weight and length. The factors of fetal presentation, placental location, amniotic fluid volume, fetal gender, gestational age, parity, or those of examiner did not seem to impact EFW accuracy in our study.

The time interval between sonographic weight estimation and delivery (shorter than 7 days), maternal BMI over 30 kg/m2, maternal age, neonatal weight and length are all factors significantly associated with the accuracy of ultrasound-based fetal weight estimation (Tab. 2, Ref. 13). Text in PDF www.elis.sk Keywords: ultrasound, biometry, fetal weight estimation.