721 Randomized trial of fundal height versus point-of-care ultrasound during routine antenatal visits

Abstract

Given the readily available point of care ultrasound (POC-US), we sought to determine whether it can replace fundal height (FH) evaluation in routine prenatal care. Pregnant women with uncomplicated singleton gestation between 22-32 weeks were randomly assigned to either a strategy of exclusive POC-US or FH for assessment at each antenatal visit. Before initiation of the study, all clinic providers were trained and certified for POC-US measurement of abdominal circumference (AC) and deepest vertical pocket (DVP). Patients were referred for a formal ultrasound if at any prenatal visit the FH differed by 3 cm or more from the patient’s gestational age in the FH group or the AC was less than the 10th or more than the 90th percentile, or the DVP was less than 2 or more than 8 cm in the POC-US group. Primary outcome was the proportion of patients who required formal USG that resulted in normal finding. We planned a traditional frequentist analysis with log-binomial regression, and estimated that 143 patients per arm would be needed to provide an 80% power to show a 30% reduction in unnecessary USG. The trial was stopped early because of the COVID-19 pandemic. A Bayesian analysis was then performed with a pre-specified probability of benefit ≥60% as evidence to resume the trial. A total of 177 pregnant patients were randomized (Table 1). Primary outcome was not different between the 2 groups (16% in the POC-US group vs 14% in the FH group). Bayesian analysis using a neutral prior centered at RR of 1 with 95% credible interval of 0.25-4 (a priori assumption: 50-50 chance that either group will be better) showed RR: 0.89 (95% CrI, 0.46-1.74) comparing FH to POC-US group, with a probability of reduced primary outcome of 63% with FH compared to POC-US. POC-US is unlikely to be better than FH for prenatal follow up. A larger study may have a higher probability that FH will outperform POC-US rather than the reverse.View Large Image Figure ViewerDownload Hi-res image Download (PPT)