Clinical estimation of fetal weight and the Hawthorne effect

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Abstract

Objective

The Hawthorne effect refers to improvement in performance solely due to the subject's knowledge that he or she is being studied. We sought to determine if an obstetrician's clinical estimation of fetal weight (EFW) is influenced by the Hawthorne effect seen in some clinical trials.

Study design

We compared obstetricians’ clinical EFW's obtained during a study period to those obtained prior to the study period in one institution. We included any patient presenting at ≥37 weeks gestation. We excluded multiple pregnancies and patients with a recent sonographic EFW.

Results

There was no difference in regards to the proportion of EFW's within 10% of the birthweight (67.9% vs. 68.5%, p = .91), the mean absolute difference of EFW-birthweight (282 ± 227 g vs. 285 ± 232 g, p = .88), or the mean absolute percent error (8.5 ± 7.4% vs. 8.6 ± 7.2%, p = .96). We also could not find any Hawthorne effect when we excluded resident physicians’ EFW's and when we analyzed the subgroup of newborns with a birth weight ≥4000 g.

Conclusion

An obstetrician's knowledge that he or she is being studied is unlikely to improve clinical EFW accuracy. Published clinical EFW accuracies are likely to be similar to those obtained in clinical practice.

Introduction

When performing and analyzing prospective clinical trials, investigators recognize the possible contribution of a placebo effect to the results of the trial [1]. The placebo effect refers to an improvement in outcomes solely from receiving treatment, even if it is an inert drug or sham surgery. A somewhat related phenomenon is the Hawthorne effect. The Hawthorne effect refers to improvement in performance solely due to the subject's knowledge that he or she is being studied [2]. The Hawthorne effect received its name from a factory called the Hawthorne Works, where a series of experiments were performed between 1924 and 1932 initially studying the effect of lighting on workers’ productivity. Whether the Hawthorne effect is real or a myth has been debated in the literature [3], [4]. However, there have been prospective studies demonstrating the Hawthorne effect on patients [5]. Additionally, the Hawthorne effect has been used to explain physician behavior in regards to patient assessment [6], prescribing patterns [7], emergency room care [8], and certain birth outcomes [9], [10].

It is possible that a physician's diagnostic accuracy can also be subject to the Hawthorne effect. Namely, if a physician were participating in a study, it is possible that he or she could knowingly or unknowingly become more accurate in diagnosing a condition based on the physical examination.

In term pregnant patients, an estimated fetal weight (EFW) is an important part of the obstetrician's assessment of the patient [11], [12]. While this can be done by ultrasound, numerous studies have shown that an obstetrician's clinical EFW, which is obtained by physical examination of the maternal abdomen, has similar accuracy compared to ultrasound [13], [14], [15], [16]. However, each of these studies was done prospectively. Therefore, it is possible that the obstetricians’ EFW accuracy was improved by the knowledge that they were being studied and that an obstetrician's EFW accuracy would be reduced in a non-investigational setting. The goal of this study was to determine if there is a Hawthorne effect in regards to a physician's clinical estimation of fetal weight in term pregnancies.

Section snippets

Methods

Obstetricians on our Labor and Delivery unit were asked to participate in a study evaluating the accuracy of their clinical EFW performed at the beginning of labor compared to their clinical EFW performed at the end of labor. The results of this particular study are published separately [17]. The obstetricians were asked to perform a clinical EFW on their patients when the patient was admitted to the labor floor at or beyond 37 0/7 weeks gestation with spontaneous labor or ruptured membranes,

Results

Obstetricians contributed EFW measurements of 187 cases and 187 controls. A greater proportion of the cases were attending obstetricians as compared to the control obstetricians (89% vs. 53%, respectively, p < .0001). Otherwise, there was no difference with respect to maternal height, weight, body mass index (BMI), cervical dilation at the time of the EFW, membrane status (intact or ruptured), fetal gender, or actual newborn birth weight (Table 1).

Comparing the EFW's before the study period

Discussion

In this study, an obstetrician's clinical estimation of fetal weight before or at the beginning of labor was not improved in a study-setting compared to a typical setting. Thus, we could find no Hawthorne effect. It would seem reasonable to conclude that the published accuracies of clinical EFW's from other prospective studies are likely to be similar to EFW's obtained in clinical practice.

This study was not designed to determine if the Hawthorne effect alters the conclusion that a clinical EFW

References (17)

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