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. 2021 Sep 7;11(9):e047188. doi: 10.1136/bmjopen-2020-047188

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© Author(s) (or their employer(s)) 2021. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.

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Ultrasound determination of the fetal head descent/progression. Placement of the transducer in the infrapubic translabial sagittal plane (A) and infrapubic transverse plane (B). (C) Measurement of the progression angle between the long axis of the pubic symphysis and a line extending from its most inferior portion tangentially to the fetal skull. (D) Measurement of the direction angle as the angle between the major longitudinal axis of the fetal head (perpendicular to the biparietal diameter) and the infrapubic line. (E) Measurement of the progression distance as the minimal distance between the infrapubic line and the leading part of the fetal skull (star). (F) Measurement of the head to perineum distance as the shortest distance from the skin surface of the perineum to the outer bony limit of the fetal skull.