Automated labour ultrasound angles sometimes miss by tens of degrees: referring the most suspicious 5% cuts gross errors from 1.2% to 0.2%
Automated angle-of-progression (AoP) measurement from intrapartum ultrasound is accurate to a few degrees on average, yet a small fraction of frames fails silently by tens of degrees. On the 501 test files of the public IUGC2025 benchmark, an ensemble of six landmark detectors ranked frames by disagreement between detectors; referring the most suspicious 5% for manual review lowered the share of errors above 20 degrees among retained frames from 1.2% to 0.2%, catching five of six. The missed case was one all six detectors underestimated with little spread between them; no difference was detected between angle-space and coordinate-space disagreement at the primary endpoint, and thresholds set on validation frames did not hold their intended referral rate on test frames.