Comparing the relation between ultrasound‐estimated fetal weight and birthweight in cohort of small‐for‐gestational‐age fetuses

Abstract

Introduction Small‐for‐gestational‐age (SGA) confers a higher perinatal risk of adverse outcomes. Birthweight cannot be accurately measured until delivery, therefore accurate estimated fetal weight (EFW) based on ultrasonography is important in identifying this high‐risk population. We aimed to establish the sensitivity of detecting SGA infants antenatally in a unit with a selective third‐trimester ultrasound policy and to investigate the association between EFW and birthweight in these babies. Material and methods A retrospective cohort study was conducted on non‐anomalous singleton pregnancies delivered after 36 weeks of gestation where SGA (<10th percentile) was diagnosed at delivery. The EFW at the time of the third‐trimester ultrasound scan was recorded using standard Hadlock formulae. Results In 2017, there were 8392 non‐anomalous singleton pregnancies live born after 36 weeks, excluding late bookers. 797 were live‐born SGA <10th percentile for birthweight and 464 <5th percentile, who met our inclusion criteria. The antenatal detection rate of SGA was 19.6% for babies with birthweight <10th percentile and 24.1% <5th percentile. There was a significant correlation between the EFW and birthweight of fetuses undergoing ultrasound assessment within 2 weeks of delivery (P < .001, r = 0.73 (Pearson correlation). For these cases, EFW was greater than the birthweight in 65% of cases. After adjusting all EFWs using the discrepancy between EFW and actual birthweight for those babies born within 48 hours of the scan, the mean difference between the birthweight and adjusted EFW 7 days before delivery was 111 g (95% CI 87‐136 g) and at 14 days was 200 g (95% CI 153‐248 g). Despite adjusting the EFW, 61/213 cases (28.6%) apparently lost weight between the ultrasound scan and delivery. Conclusions Small‐for‐gestational‐age infants with a birthweight <10th percentile are poorly identified antenatally with little improvement for those <5th percentile. In SGA babies, ultrasound EFW overestimated birthweight. Discrepancies between birthweight and EFW are not explicable only by the limitations of third‐trimester sonography, a reduction in fetal weight close to delivery in a proportion of liveborn SGA babies is plausible.

Ultrasound estimation of fetal weight accuracy in a regional hospital: A retrospective audit

“…While Barel et al 18 reported that fetal sex, presentation and AFI did have a significant effect on EFW (reported as mean PE), they suggested that their contribution was small and of uncertain clinical consequence. Overestimation of smaller fetuses has been reported 23,28,29 and although there was no significant association between birthweight category and accuracy in our sample, there was a tendency to overestimate across all categories, but more so in the low (mean AE 8.1%) and macrosomic birthweight categories (mean AE 7.1%) compared to the normal birthweight category (mean AE 6.1%). This overestimation is consistent with Campbell Westerway 19 who compared six commonly used ultrasound EFW formulae against the 1999 Australian birthweights and demonstrated that after 37 weeks GA, EFW significantly overestimated the birthweight and the highest random error occurred in macrosomic fetuses.…”

Relationship Between Maternal Serum Cortisol and Maternal Insulin Resistance and Fetal Ultrasound Characteristics in Gestational Diabetes Mellitus

“… 36 Although EFW is an indirect estimate of actual fetal weight and is generally overestimated in 65% of the cases, EFW is strongly correlated with actual weight at 2 weeks before birth. 37 Therefore, race might contribute to the difference among studies on the correlation between maternal cortisol and fetal development. Besides, the method for collecting and interpreting serum cortisol could lead to the difference.…”

Maternal and fetal characteristics to predict c-section delivery: A scoring system for pregnant women

“… 14 , 30 Another previous study also supports our finding, suggesting that a total of 60.7% of pregnancies with a fetal weight more than 3500 were delivered by c-section, compared to 39.3% for a fetus weighing < 3500 g. 28 Although our study used the clinical birthweight rather than the estimated fetal weight, previous studies have found that there was no significant difference between estimated fetal weight and actual birth weight in normal weight population. 31 Significant difference of fetal weight usually found in small for gestational age fetus, with differences up to 200 g. 32 Thus, a clinically-determined estimated fetal weight of ⩾ 3500 g, can still be a predictive factor for an increased risk of c-section. In addition, our study also found that non-cephalic presentation is associated with increased risk of c-section.…”