Accuracy and reliability of ultrasound estimation of fetal weight in women with a singleton term pregnancy

Abstract

Background: Prenatal estimation of birth-weight is of utmost importance to predict the mode of delivery. This is also an important parameter of antenatal care. This study was conducted to evaluate the accuracy of estimated fetal weight by ultrasound, compared with actual birth weight.Methods: This was a prospective and comparative study comprising 110 pregnant women at term. Patients who had their sonography done within 7 days from date of delivery were included. Fetal weight was estimated by Hadlock 2 formula, the software of which was preinstalled in ultrasound-machine. The estimated fetal weight was compared to the post-delivery birth-weight. The Pearson's correlation coefficient was used and the accuracy of sonographic fetal weight estimation was evaluated using mean error, mean absolute error, mean percentage error, mean absolute percentage error and proportion of estimates within 10% of actual birth weight.Results: Mean estimated and actual birth weights were 3120.8±349.4 gm and 3088.2±404.5 g respectively. There was strong positive correlation between estimated fetal weight and actual birth weight (r = 0.58, p<0.001). The mean percentage error and mean absolute percentage error of ultrasound fetal weight estimations were 1.96±11.8% and 8.7±8.2% respectively. The percentage of estimates within ±10% of the actual birth weight was found to be 67.3%. In 23% of the cases, ultrasound overestimated the birth weight. In 13% of the cases, ultrasound underestimated the birth weight.Conclusions: There was strong positive correlation between actual and sonographically estimated fetal weight. So, ultrasonography can be considered as useful tool for estimating the fetal weight for improving the perinatal outcome.

Accuracy of ultrasound in estimating fetal weight in New Zealand

“…The proportion of fetal weight estimations at our institution that were outside the acceptable 10% variation was similar to previous studies with just over three out of four (75.9%) being within 10% of the recorded birth weight at delivery 1,2,5–8 . A retrospective audit from Wellington Hospital in 2006 also reported an accuracy of 75% 7 .…”

“…Other studies prior to 2006 reported fetal weight estimation accuracies that varied between 23 and 78%, 6 but few of these distinguished between overestimated and underestimated group features. More recent studies from other countries have similar degrees of accuracy to ours but they have different population demographics such as lower mean maternal ages, weights and normal range BMI, 5,9 compared with our average BMI of 27kg/m 2 which is classified as overweight.…”

“…Underestimating birthweight category leads to under recognition of LGA age babies who are at higher risk for perinatal morbidity, with the increased risk of asphyxia due to prolonged delivery, shoulder dystocia, brachial plexus injury as well as maternal adverse outcomes such as increased rates of emergency caesarean section, perineal injuries and post‐partum haemorrhage associated with birth. Our group of SGA fetuses in whom US overestimated both the EFWs and categories in 18 (40% of SGA by birthweight) raises even more concern, a trend also demonstrated by Sharma et al 5 This kind of overestimation can result in failure to recognise SGA babies who are at increased risk of still birth. These fetuses can miss out on appropriate referral to the multidisciplinary team which would consider care involving closer monitoring with regular Doppler US, the need for steroid preparation, consideration for early delivery that may be necessary for survival and neonatal specialist support at delivery.…”

Accuracy of ultrasound in the estimation of customised birth weight in a public hospital service

“…The overall accuracy of ultrasound in estimating foetal weight at this obstetric ultrasound service was within 15% of birth weight for 92%, and within 10% of birth weight for 77% of scans performed within 7 days of birth. These findings are similar to local and international data 7,12,13 . Accuracy (±15%) was lowest for SGA babies (87%) and highest for AGA babies (93%).…”

“…These findings are similar to local and international data. 7,12,13 Accuracy (AE15%) was lowest for SGA babies (87%) and highest for AGA babies (93%). Similarly, sensitivity was lowest for SGA at 51% while adequate for AGA and LGA babies (83% and 82%).…”