Research over the last 3 decades has consistently disagreed on the best method (clinical examination, Leopold's maneuvers or ultrasound imaging), for estimating fetal weight in the third trimester (Dudley, 2005). Estimation, and ultimately prediction, of fetal weight could be optimized to guide care during the latter part of pregnancy. Physicians and midwives use fetal weight estimation to decide the optimal mode and timing of birth to minimize risk of birth trauma and shoulder dystocia.
A large, prospective blinded observational study found that ultrasound outperforms Leopold's maneuvers with a lower absolute error in fetal weight estimation at greater than 37 weeks' gestation (Preyer et al., 2019). Though ultrasound can provide lower error estimates than Leopold's maneuvers, a meta-analysis of 29 studies found that ultrasound measurements alone only have a sensitivity of 56% and specificity of 92% for predicting birthweights for large for gestational age (Malin et al., 2016). Current evidence suggests that both Leopold's maneuvers and ultrasound measurements alone are not sufficient for accurate estimation of fetal weight in the third trimester. The American College of Obstetricians and Gynecologists' (2020) practice bulletin on macrosomia acknowledges the imprecision of fetal weight estimation but states that ultrasound can be used to rule out macrosomia although it is no better than abdominal palpation for this purpose.
In the clinical setting, we often encounter patients who feel pressured to make a decision about a 39-week induction of labor due to suspicion of a large for gestation fetus in the context of an otherwise low-risk, healthy pregnancy. A systematic review found patients' preferences are largely unmet and decision-making is driven by medical considerations (Coates et al., 2020). If we are providing guidance to patients about labor care and self-management of early labor symptoms, we need to contextualize estimated fetal weight as a single data point that is informed by the full clinical picture. Maintaining patient autonomy and transparent health care is critical at a point in pregnancy where patients can be misguided under the guise of maintaining the health of the baby. Ultimately, a healthy and happy family includes the mental and physical wellbeing of both patients.
New technology gives promise to the potential of use of fetal weight as a component of decision-making and guidance during pregnancy and labor. Data science methods have been used in other fields such as radiology and cardiology to overcome challenges in measurement, assessment, and clinical prediction using images. In pregnancy, algorithms using ultrasound have been used to detect fetal anomalies and recognize maternal and fetal anatomical planes. Future work should consider how we can use both ultrasound imaging and clinical examination to make better estimation. All technology should be held to the highest level of discernment and evidence quality before routine use. Leveraging large-scale data with active listening and hands-on examination, together, could move practice on estimation of fetal weight in late pregnancy toward the reduction of inaccurate estimation of fetal weight that can lead to unnecessary cesarean births, contributing to cesarean birth-related maternal morbidity and mortality.
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