Objective: To establish whether the degree of clinician bias in fundal height measurement is affected by patient body mass index (BMI) or provider experience.
Methods: Singleton, ultrasound-dated pregnancies between 24 weeks and 40 weeks underwent fundal height measurements (n=103) by two providers, each using one blank and one marked measuring tape. Outcomes were the differences between the blank and marked measurements (bias) and between fundal height and gestational age for blank and marked tapes. Mixed models for repeated measures (provider and tape type) were used to estimate outcomes and compare them according to provider experience level and for patient background and anthropometric characteristics.
Results: Bias increased with patient BMI, although only among providers with less than 2 years of experience (juniors, P=.004) and not for those with more experience (seniors, P=.38). Similarly, bias decreased over the study enrollment period among junior, but not senior providers. Providers of all levels were more likely to measure a fundal height within 3 cm of gestational age using a marked tape than a blank tape (odds ratio 1.83, 95% confidence interval 1.41-2.38).
Conclusion: Clinicians are biased in their fundal height measurements by knowledge of gestational age and use of a marked measuring tape. This tendency increases with higher patient BMI and with less provider experience.