There are 4, not 7, cardinal movements in labor

Abstract

The mechanics of labor describe the forces required for fetal descent, and the movements that the fetus must perform to overcome the resistance met by the maternal bony pelvis and soft tissue. The fetus negotiates the birth canal and rotational movements are necessary for descent. Anglo-American literature lists 7 cardinal movements, namely engagement, descent, flexion, internal rotation, extension, external rotation, and expulsion. German and older English literature lists only 4 rotational movements as the cardinal movements and excludes engagement, descent, and expulsion. We would argue that descent is the main purpose of the uterine powers and cardinal movements, a description of the rotational movements the fetal head and shoulders must perform to obtain descent. Ultrasound offers a historically unique opportunity for noninvasive, dynamic studies of the mechanics of labor. The information gathered by clinical examination and ultrasound should be integrated into clinical decision making. The mechanics of labor describe the forces required for fetal descent, and the movements that the fetus must perform to overcome the resistance met by the maternal bony pelvis and soft tissue. The fetus negotiates the birth canal and rotational movements are necessary for descent. Anglo-American literature lists 7 cardinal movements, namely engagement, descent, flexion, internal rotation, extension, external rotation, and expulsion. German and older English literature lists only 4 rotational movements as the cardinal movements and excludes engagement, descent, and expulsion. We would argue that descent is the main purpose of the uterine powers and cardinal movements, a description of the rotational movements the fetal head and shoulders must perform to obtain descent. Ultrasound offers a historically unique opportunity for noninvasive, dynamic studies of the mechanics of labor. The information gathered by clinical examination and ultrasound should be integrated into clinical decision making. The mechanics of labor describe the forces required for fetal descent and the movements the fetus must perform to overcome the resistance met by the maternal bony pelvis and soft tissue, mainly the levator ani muscle and the pelvic floor. The pelvic inlet is at a 90-degree angle to the pelvic outlet, forming a curved canal with varying diameters. The 3 sections of the birth canal are the inlet, the cavity, and the outlet. In the gynecoid pelvis, the inlet is widest in the transverse and the cavity more rounded, whereas the outlet is widest in the anterior-posterior diameter. The critical diameters in a human fetus are the head and the shoulders, and the fetus must rotate to negotiate the birth canal. These rotational movements of the fetal head and shoulders are often called the cardinal movements, but in earlier publications they are usually only referred to as movements.1Schaeffer O. Labor and operative obstetrics. W.B. Saunders & Company, London, England, and Philadelphia, PA1901Google Scholar, 2Shears GP. Obstetrics, normal and operative.6th ed. J.B. Lippincott Publishers Company, Philadelphia, PA, and London, England1929Google Scholar, 3Spiegelberg O. Lehrbuch der Geburtshülfe (classic reprint). Forgotten Books, London, England2019Google Scholar German and older English literature lists 4 movements as the cardinal movements.4Galabin AL. A manual of midwifery.4th ed. J. & A. Churchill, London, England1897Google Scholar, 5Kerr JMM. Operative obstetrics.4th ed. Bailliere, Tindall and Cox, London, England1937Google Scholar, 6Pschyrembel W. Praktische Geburtshilfe. Walter de Gruyter, Berlin, Germany1947Crossref Google Scholar In a gynecoid pelvis, the fetal head usually enters the pelvis in a transverse position, and the first rotational movement in the long axis of the fetus is flexion of the neck (Figure 1). The second movement is a transverse rotation of the occiput anteriorly (Figure 2), and the fetus is then facing the mother's back with the fetal head oriented in the anterior-posterior direction. This allows exit of the fetal head through the pelvic outlet, which is the largest in the anterior-posterior diameter. This second rotation allows the shoulders to enter the inlet of the pelvis in the transverse plane. When the nape of the fetal neck passes beneath the maternal symphysis, the resistance from the maternal soft tissue pushes the fetal head upwards, creating an extension of the head. This movement is called the third rotational movement (Figure 3, Video). The fourth movement is the external rotation (Table). The fetal body and shoulders are now in the middle of the pelvis and can rotate into the largest anteroposterior plane of the outlet. As this happens, the fetal head rotates to face the mother's right or left thigh. (Figure 4).Figure 2Occiput at 8.30 (transabdominal scan), 10.30 and at 12 o'clock (transperineal scan) from left to rightIversen. There are 4 cardinal movements in labor. Am J Obstet Gynecol MFM 2021.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Figure 3Head extension shown with sagittal transperineal scanning shortly before deliveryIversen. There are 4 cardinal movements in labor. Am J Obstet Gynecol MFM 2021.View Large Image Figure ViewerDownload Hi-res image Download (PPT)TableThe 4 classical cardinal rotational movementsIversen. There are 4 cardinal movements in labor. Am J Obstet Gynecol MFM 2021.1. Flexion of the fetal head2. Internal rotation3. Extension of the fetal head4. External rotation for the shoulders Open table in a new tab Figure 4The images show extension of the neck (third movement), followed by rotation of the shoulders (fourth movement), and expulsion of the fetusIversen. There are 4 cardinal movements in labor. Am J Obstet Gynecol MFM 2021.View Large Image Figure ViewerDownload Hi-res image Download (PPT) Understanding the cardinal movements of the fetal head is a relatively recent development in medicine. These are not described in ancient texts, which focus on lie and presentation,7Potter P. Hippocrates volume XI. Harvard University Press, Cambridge, MA2018Google Scholar,8Ephesus SO Temkin O. Soranus’ gynecology. Johns Hopkins University Press, Baltimore, MD1956Google Scholar however, Soranus mentions that the birth is even more favorable when the fetus descends with its face turned downward.8 William Smellie in “A Treatise on the Theory and Practice of Midwifery” infers knowledge of the cardinal movements, but does not name them.9Smellie WMD. Smellie's treatise on the theory and practice of midwifery.Edinb Med J. 1877; 22: 812-815Google Scholar In Alfred Galabin's “A Manual of Midwifery,” the term “cardinal movements” appears4Galabin AL. A manual of midwifery.4th ed. J. & A. Churchill, London, England1897Google Scholar and is adopted by later authors such as Munro Kerr.5Kerr JMM. Operative obstetrics.4th ed. Bailliere, Tindall and Cox, London, England1937Google Scholar In the German tradition, Spiegelberg from Breslau lists the following 4 “movements” in 1878: flexion, internal rotation, extension, and external rotation, and in Pschyrembel's “Practische Geburtshilfe” from 1947, these 4 movements are called cardinal movements.3Spiegelberg O. Lehrbuch der Geburtshülfe (classic reprint). Forgotten Books, London, England2019Google Scholar,6Pschyrembel W. Praktische Geburtshilfe. Walter de Gruyter, Berlin, Germany1947Crossref Google Scholar In the United States, Shears’ “Obstetrics, Normal and Operative” talks of “movements of the head” and lists 5 movements, namely flexion, descent, rotation, extension, and external rotation.2Shears GP. Obstetrics, normal and operative.6th ed. J.B. Lippincott Publishers Company, Philadelphia, PA, and London, England1929Google Scholar In “Willams Obstetrics,” third edition, J. Whitridge Williams writes that the 3 true cardinal movements are descent, internal rotation, and flexion, whereas extension and external rotation are only accessory movements,10Williams JW A text-book for the use of students and practitioners.3rd ed. D. Appleton and Company, New York, NY1912Google Scholar and in the 10th edition, editor J. Nicholson opines that the 3 cardinal movements are in fact descent, internal rotation, and extension, whereas flexion and external rotation are now considered accessory movements.11Eastman NJ. Williams obstetrics.10th ed. Appleton-Century-Crofts, Inc, New York, NY1950Google Scholar By the 1989 edition, edited by F. Cunningham, the list of cardinal movements had increased to 7.12Cunningham FG MacDonald PC Gant NF Williams JW. Williams obstetrics.18th ed. Appleton & Lange, Norwalk, CT1989Google Scholar Engagement is called the first movement. Descent is the gradual passage of the fetus through the birth canal and is called the second movement. The next 4 movements are the rotational movements described above and expulsion of the fetus is called the seventh movement. The 3 extra movements listed in “Williams Obstetrics,” refer to fetal descent. Engagement is simply a stage of descent when the largest diameter of the fetal head has passed the pelvic inlet and expulsion the ultimate result of the descent. One could argue that descent of the fetal head is an obligate movement without which the fetus cannot be born, as “Williams Obstetrics” and some earlier authors do.10Williams JW A text-book for the use of students and practitioners.3rd ed. D. Appleton and Company, New York, NY1912Google Scholar, 11Eastman NJ. Williams obstetrics.10th ed. Appleton-Century-Crofts, Inc, New York, NY1950Google Scholar, 12Cunningham FG MacDonald PC Gant NF Williams JW. Williams obstetrics.18th ed. Appleton & Lange, Norwalk, CT1989Google Scholar, 13Scanzoni FW: Geburtshilfe. Wien: verlag Von L.W.Seidel 1854.Google Scholar However, we would argue that descent is the main purpose of the uterine powers, and the cardinal movements are a description of the rotational movements the fetal head and shoulders must perform to obtain descent. This is a descriptive discussion without any direct clinical value, but understanding the rotational movements is of clinical importance. The 4 classic rotational movements listed above only occur with the fetus delivering in an occiput anterior (OA) position in a gynecoid pelvis. An anthropoid pelvis has a pelvic inlet that is widest in the anterior-posterior diameter. The rotational movements in the anthropoid pelvis must be different from that of a gynecoid pelvis, however, the labor mechanics in pelvic forms other than in the gynecoid pelvis is vastly understudied. The cardinal movements vary with fetal head position and attitude (degree of flexion). If the internal rotation (second cardinal movement) leads to an occiput posterior (OP) position, the third cardinal movement is maximal flexion followed by an extension to a neutral attitude after the head is born. Even if maximally flexed, the fetus in OP position can never follow the curve of the birth canal as optimally as the fetus in OA position does through extension. This is of vital importance for the clinicians to understand, because traction used in assisted deliveries must differ from that used in OA position. As the head reaches the pelvic floor, the fetus in OP position must continue straight forward for longer before upwards traction is possible when compared with the fetus in OA position.14Ghi T Maroni E Youssef A et al.Sonographic pattern of fetal head descent: relationship with duration of active second stage of labor and occiput position at delivery.Ultrasound Obstet Gynecol. 2014; 44: 82-89Crossref PubMed Scopus (42) Google Scholar If the clinician, instead of continuing straight forward, overcorrects with downwards traction, the risk of an anal sphincter tear greatly increases.5Kerr JMM. Operative obstetrics.4th ed. Bailliere, Tindall and Cox, London, England1937Google Scholar,15Dennen ED. Forceps deliveries.2nd ed. F.A. Davis Company, Philadelphia, PA1964Google Scholar OP deliveries are associated with more failed deliveries. This may, in part, be because the OP fetus goes undiagnosed, but also because the OP fetus generally presents less flexed throughout the delivery than a fetus in OA position and because clinicians are not well versed in the differences in labor mechanics. If an OP position can be corrected to an OA position through rotational vacuum, forceps, or manual rotation, it is advantageous for ease of delivery. Manual rotation is currently gaining popularity, but a randomized study was underpowered to show reduced operative delivery rates.16Phipps H Hyett JA Kuah S et al.Persistent occiput posterior position outcomes following manual rotation: a randomized controlled trial.Am J Obstet Gynecol MFM. 2021; 3100306Abstract Full Text Full Text PDF PubMed Scopus (5) Google Scholar Another randomized clinical trial found reduced risk of operative delivery after prophylactic manual rotation of OP or occiput transverse positions during the early second stage of labor.17Blanc J Castel P Mauviel F et al.Prophylactic manual rotation of occiput posterior and transverse positions to decrease operative delivery: the PROPOP randomized clinical trial.Am J Obstet Gynecol. 2021; ([Epub ahead of print])PubMed Google Scholar To successfully perform instrumental or manual rotations, precise diagnostics of fetal head station, position, and flexion is necessary. Fetal attitude and position are difficult to assess with clinical examinations in the early phase of labor, but easy to see with ultrasound. Therefore, ultrasound can increase the understanding of labor mechanics and help clinicians in decision making. Fetal rotation has recently been described longitudinally with ultrasound in nulliparous women with a spontaneous onset of labor, and 85% followed the 4 classical movements, but with the varying length of the internal rotation (second movement) depending on the initial position.18Hjartardóttir H Lund SH Benediktsdóttir S Geirsson RT Eggebø TM. When does fetal head rotation occur in spontaneous labor at term: results of an ultrasound-based longitudinal study in nulliparous women.Am J Obstet Gynecol. 2021; 224 (514.e1–9)Abstract Full Text Full Text PDF Scopus (6) Google Scholar Fetal attitude can be measured (Figure 1),19Bellussi F Livi A Cataneo I Salsi G Lenzi J Pilu G. Sonographic diagnosis of fetal head deflexion and the risk of cesarean delivery.Am J Obstet Gynecol MFM. 2020; 2100217Abstract Full Text Full Text PDF PubMed Scopus (8) Google Scholar, 20Eggebø TM Heien C Okland I et al.Prediction of labour and delivery by ascertaining the fetal head position with transabdominal ultrasound in pregnancies with prelabour rupture of membranes after 37 weeks.Ultraschall Med. 2008; 29: 179-183Crossref PubMed Scopus (26) Google Scholar, 21Ghi T Bellussi F Azzarone C et al.The ”occiput-spine angle”: a new sonographic index of fetal head deflexion during the first stage of labor.Am J Obstet Gynecol. 2016; 215 (84.e1–7)Abstract Full Text Full Text PDF PubMed Scopus (29) Google Scholar and fetal position can be described like a clock face with 12 or 24 divisions (Figure 2).22Akmal S Tsoi E Kametas N Howard R Nicolaides KH. Intrapartum sonography to determine fetal head position.J Matern Fetal Neonatal Med. 2002; 12: 172-177Crossref PubMed Scopus (157) Google Scholar The “head up sign” means that the fetal neck is extended and the head is directed upward in the pelvic outlet.23Henrich W Dudenhausen J Fuchs I Kämena A Tutschek B. Intrapartum translabial ultrasound (ITU): sonographic landmarks and correlation with successful vacuum extraction.Ultrasound Obstet Gynecol. 2006; 28: 753-760Crossref PubMed Scopus (153) Google Scholar Figure 3 shows a fetus with an extended neck shortly before delivery. Ultrasound is redundant to assess the fourth movement (Figure 4). Ultrasound has the potential to add clinically important information, but information alone is not enough to improve outcomes.24Ramphul M Ooi PV Burke G et al.Instrumental delivery and ultrasound: a multicentre randomised controlled trial of ultrasound assessment of the fetal head position versus standard care as an approach to prevent morbidity at instrumental delivery.BJOG. 2014; 121: 1029-1038Crossref PubMed Scopus (71) Google Scholar Understanding how to use the information is essential.25Gladwell M. Blink: the power of thinking without thinking. Penguin, London, England2006Google Scholar,26Youssef A Pilu G. Knowledge, understanding and fetal occiput position.Ultrasound Obstet Gynecol. 2016; 47: 523-524Crossref PubMed Scopus (10) Google Scholar To translate the information gathered by clinical examination and ultrasound into clinical decision making, a deeper understanding of labor mechanics is required. Unfortunately, this knowledge is not easily accessible anymore, because the topic is reduced to superficial sections in most modern textbooks. Most research on labor mechanics is more than 50 years old, and we believe a revival is long overdue, because there are still unanswered questions. Ultrasound offers a historically unique opportunity for noninvasive, dynamic studies of the mechanics of labor to answer those questions. We would like to thank our previous supervisors Kåre Augensen and Per Børdahl for teaching us the mechanics of labor and adding important information to this article. https://www.ajogmfm.org/cms/asset/edd4f19d-c7af-4b0d-b1a9-2613420c1c1d/mmc1.mp4Loading ... Download .mp4 (0.39 MB) Help with .mp4 files Video Head extension shown with sagittal transperineal scanning short time before deliveryhttps://www.ajogmfm.org/cms/asset/83d54da2-2ba2-47df-b6cf-2f4e7e1eaae0/mmc2.mp4Loading ... Download .mp4 (7.04 MB) Help with .mp4 files

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