Israel Medical Association Journal

Background: The sonographic assessment of estimated fetal weight (EFW) is essential for identification of fetuses in weight extremes and aids in peripartum management. However, there are inconsistent reports regarding EFW accuracy.

Objective: To examine maternal and fetal determinants associated with unreliable EFW.

Methods: A retrospective case-control study was conducted at a single, tertiary medical center between 2011 and 2019. All term, singleton deliveries with a sonographic EFW within 2 weeks of delivery were included. Unreliable EFW was defined as > 500 grams discordance between it and the actual birth weight. We allocated the study cohort into two groups: unreliable EFW (cases) and accurate EFW (controls).

Results: Overall, 41,261 deliveries met inclusion criteria. Of these, 1721 (4.17%) had unreliable EFW. The factors positively associated with unreliable EFW included body mass index > 30 kg/m², weight gain > 20 kg, higher amniotic fluid index, pregestational diabetes, gestational age > 41^0/7, and birth weight ≥ 4000 grams. On multiple regression analysis, pregestational diabetes (odds ratio [OR] 2.22, 95% confidence interval [95%CI] 1.56–3.17, P < 0.001) and a higher birth weight (OR 1.91, 95%CI 1.79–2.04, P < 0.001) were independently associated with unreliable EFW. On analysis of different weight categories, pregestational diabetes was associated with unreliable EFW only among birth weights ≥ 3500 grams (OR 3.28, 95%CI 1.98–5.44, P< 0.001) and ≥ 4000 grams (OR 4.27, 95%CI 2.31–7.90, P < 0.001).

Conclusion: Pregestational diabetes and increased birth weight are independent risk factors for unreliable EFW and should be considered when planning delivery management.

Background: Two types of growth curves are commonly used to diagnose fetal growth disorders: neonatal birth weight (BW) and sonographic estimated fetal weight (EFW). The debate as to which growth curve to use is universal.

Objectives: To establish sonographic EFW growth curves for the Israeli population and to assess whether the use of the BW growth curves currently adapted in Israel leads to under-diagnosis of intrauterine growth disorders.

Methods: Biometric data collected during a 6 year period was analyzed to establish sonographic EFW growth curves between 15–42 weeks of gestation for the Israeli population. Growth curves were compared to previously published sonographic EFW growth curves. A comparison with the Israeli BW growth curves was performed to assess the possibility of under-diagnosis of intrauterine growth disorders.

Results: Out of 42,778 sonographic EFW studies, 31,559 met the inclusion criteria. The sonographic EFW growth curves from the current study resembled the EFW curves previously published. The comparison of the current sonographic EFW and BW growth curves revealed under-diagnosis of intrauterine growth disorders during the preterm period. Four percent of the fetuses assessed between 26–34 weeks would have been suspected of being growth restricted; 2.8 percent of the fetuses assessed between 30–36 weeks would have been suspected of having macrosomia, based on the BW growth curves.

Conclusions: New Israeli sonographic EFW growth curves resemble previously published sonographic EFW curves. Using BW growth curves may lead to the under-diagnosis of growth disorders. We recommend adopting sonographic EFW growth to diagnose intrauterine growth disorders.