Factors Affecting Clinical over and Underestimation of Fetal Weight-A Retrospective Cohort.

Clinical estimation of fetal weight is an integral component of obstetric care that might dictate the timing and mode of delivery. Inaccurate fetal weight estimation might result in unnecessary interventions or in underestimating potential risks, resulting in inappropriate intrapartum care. This retrospective study assessed factors associated with under- or overestimation of birthweight and evaluated the obstetric implications. It included singleton births ≥24 w with clinically estimated fetal weight (EFW) up to 1 week before delivery, during 2014-2020. Estimates >±10% of the actual birthweight were considered inaccurate and categorized as overestimation (>10% heavier than the actual birthweight) or underestimation (>10% smaller than the birthweight). Multivariable logistic regression was performed to reveal factors associated with inaccurate EFW. Maternal characteristics and obstetric outcomes were compared. The primary outcomes for the overestimation group were the neonatal composite adverse outcome, induction of labor and cesarean delivery rates. The primary outcomes for the underestimation group were rates of shoulder dystocia, 3rd- or 4th-degree perineal lacerations, and failed vacuum extraction. Among 38,615 EFW, 5172 (13.4%) were underestimated, 6695 (17.3%) were overestimated and 27,648 (69.3%) accurate. Multivariable logistic regression found increasing gestational age as an independent risk-factor for underestimation (odds ratio (OR) 1.15 for every additional week, 95% confidence interval (CI) 1.12-1.2). Major factors independently associated with overestimation were nulliparity (OR 1.95, CI 1.76-2.16), maternal obesity (OR 1.52, CI 1.33-1.74), smoking (OR 1.6, CI 1.33-1.93), and oligohydramnios (OR 1.92, CI 1.47-2.5). Underestimation was an independent risk-factor for shoulder dystocia (OR 1.61, CI 1.05-2.46) and 3rd- or 4th-degree perineal lacerations (OR 1.59, CI 1.05-2.43). Overestimation was an independent risk-factor for neonatal composite adverse outcome (OR 1.15, CI 1.02-1.3), induced labor (OR 1.30, CI 1.21-1.40) and cesarean delivery (OR 1.59, CI 1.41-1.79). Clinicians should be aware of factors and adverse obstetric implications associated with over- or underestimation of birthweight.