Assessment of modifications to a blind-sweep ultrasound protocol for improved lower-uterus imaging by novice operators

Blind-sweep ultrasound protocols may improve prenatal care in low-resource settings, but lower-uterus visualization is often insufficient when performed by novices. We evaluated three modifications to a standard protocol aimed at improving lower-uterus imaging: Step A (caudal probe tilt), Step B (caudal sweep with probe angled caudally), and Step C (caudo-cranial sweep with lower probe placement). Outcomes included fetal head visibility, number of scans with measurable head circumference (HC), and agreement with clinical HC measurements. Adding Steps A or B substantially increased fetal head visibility and the proportion of scans with measurable HC. Step A produced the largest improvement, raising scans with $$\ge 2/3$$ head visibility from 25.5% to 93.8%, and increasing measurable HC from 55.2% to 99.5% for a reader experienced in blind-sweep analysis ($$n=210$$), and from 7.8% to 74.8% in a subset ($$n=103$$) annotated by an obstetric gynecologist. These gains were concentrated in scans where the standard protocol failed to visualize the fetal head, with no significant benefit when at least partial visibility was already achieved. Bias and limits of agreement with clinical HC were similar across all variants, indicating accurate measurements when usable frames were available. Step C provided minimal improvement. Insufficient lower-uterus visualization is a frequent but easily correctable limitation of blind-sweep protocols performed with minimal supervision. A simple caudal tilt (Step A) enhances fetal head visibility and measurable HC rate, supporting its integration into standardized protocols for novices. Prospective validation in low-resource settings is needed to confirm generalizability under varying training and supervision conditions.