Fig. 3From: Accuracy of non-invasive methods for assessing the progress of labor in the first stage: a systematic review and meta-analysisThe OSA, HPD, AOP, HD and HSD of ultrasound parameters. OSA, occiput-spine angle; HPD, head-perineum distance; AOP, angle of progression; HD fetal head direction; HSD, head symphysis distanceBack to article page