Understanding Mechanisms of Normal Labor | Fetal Presentation, Attitude, and Position

1. MECHANISMS OF NORMAL LABOR Hidayat Wijayanegara

2. I. Lie, presentation, attitude and position • Fetal orientation can be established clinically : • abdominal palpation • vaginal examination • auscultation • sonography • X-Ray

3. Fetal lie • Is the relation of the long axis of the fetus to that of mother • Longitudinal - transverse - oblique • Longitudinal lies are present in over 99 percent of labor at term • Predisposing factors for transverse lie : • multi parity • placenta previa • hydramnios • uterine anomalies

4. Fetal presentation • The presenting part : • portion of the body of the fetus is either foremost within the birth canal or in proximity to it • Can be felt through the cervix on vaginal examination • Determines the presentation

5. In longitudinal lie creating cephalic and breech presentation • In transverse lie  the shoulder presentation

6. Cephalic presentation 1. The head is flexed sharply  The chin is contact with the thorax  The occipital fontanel is the presenting part  Vertex or occiput presentation

7. Cephalic presentation 2. Face presentation : Fetal neck  extended  Occiput & back come in contact  The face is foremost in the birth canal  Face presentation

8. Vertex presentation --- Face presentation • Brow presentation • Partially extended • Brow is the presenting part • Sinciput presentation • The fetal head partially flexed • Anterior/large fontanel is the presenting part . • VertexFace • presentation Transientpresentation Labor progresses Labor progresses

10. Breech presentation There are three general configuration : • Frank breech • presentation : • The thighs are flexed • The legs extended over the anterior surfaces of the body • Complete breech • presentation : • The thighs are flexed on the abdomen & the legs upon the thighs • Incomplete; • footling breech • presentation : • One or both feet/knees are lowermost

13. Fetal attitude or posture • The head is sharply flexed • The chin is almost contact with the chest • The thighs are flexed over the abdomen • The legs are bent at the knees • The arms usually crossed over the thorax  Accomodation to the uterine cavity

14. Fetal position • The relation of an arbitrarily chosen portion of the fetal presenting part to the right or left side of the maternal birth canal • Each presentation there maybe two position, right or left • The determining part of : • vertex  occiput • face  chin (mentum) • breech  sacrum

15. Varieties of presentation and position OA ROA LOA ROT LOT ROP LOP OP

20. Diagnosis of fetal presentation and position A. Abdominal palpation - Leopold maneuvers • Conducted systematically

21. B. Vaginal examination Three maneuvers : 1. Two fingers of either gloved hand are introduced into the vagina and carried up to the presenting part The differentiation : • vertex • face • breech

22. 2. If the vertex is presenting : • Sagittal suture (?) • Small & large fontanels 3. The station  is established

25. C. Auscultation Does not provide reliable information concerning fetal presentation & position D. Sonography Fetal head & body can be located

26. Labor with occiput presentation • 95% of all labors  the fetus is in the occiput or vertex presentation • In the majority of cases  the vertex enters the pelvis with the sagital suture in thetransverse pelvic diameter • Left occiput transverse (LOT) : 40% of labors • Right occiput transverse (ROT) : 20% of labors • Occiput posterior : 20% of labors

27. Cardinal movement of labor • Irregular shape of the pelvic canal • The relatively large dimensions of the mature fetal head • A process of adaptation or accomodation of suitable portion of the head to the various segments of the pelvis is required for vaginal delivery

28. The cardinal movements of labor : - engagement - extension - descent - external rotation - flexion - expulsion - internal rotation

29. For purposes of instruction, the various movement often are described as though they occurred separately and independently  in reality the mechanism of labor consists of a combination of movements that are ongoing simultaneously For example : - as part of the process of engagement  there is both flexion and descent of the head

30. Engagement : • The greatest transverse diameter (BPD) in occiput presentation, passes through the pelvis inlet • In many primigravida this phenomena may takes place during the last weeks of pregnancy • In many multiparous and some nulliparous  the fetal head is still freely movable above the pelvic inlet (floating)

31. Asyinclitism • The sagital suture, entering the pelvic inlet may not lie exactly midway between the symphysis and sacral promontory • The sagital suture deflected either posteriorly toward the promontory or anteriorly toward the symphysis • Such lateral deflection of the head to a more anterior or posterior position is called asynclitism  anterior & posteriorasynclitism

33. Descent • The first requisite for birth of the infant • In nulliparas, engagement may take place before the onset of labor  and further descent takes place at the second stage • Four forces : a. pressure of amniotic fluid b. direct pressure of the fundus upon the breech with contraction c. bearing down effort d. extension and straightening of the fetal body

34. Flexion • Resistance from the cervix, wall of the pelvis, pelvic floor  flexion of the head • The chin more contact with the fetal thorax • Suboccipito bregmatic diameter is substituted for the longer occipito frontal diameter

37. Internal rotation • The occiput gradually moves anteriorly toward the symphysis pubis or less commonly, posteriorly toward the hollow of the sacrum • Is always associated with descent • Is not accomplished until the head has reached the level of the spine and thereafter is engaged

38. Calkins (1939) • Concluded : • Two thirds  internal rotation is completed by the time the head reaches the pelvic floor • A fourth  internal rotation is completed very shortly after the head reaches the pelvic floor • 5 percent  internal rotation does not take place

39. Extension • Extension brings the base of the occiput into direct contact with the interior margin of the symphysis pubis • Causes of extension : • The vulva outlet is directed upward and forward

40. Two forces come into play : a. Exerted by the uterus  act more posteriorly b. Resistant pelvic floor and the symphysis acts more anteriorly  the resultant vector is in the direction of the vulva opening  causing extension

41. External Rotation • The delivered head next undergoes restitution • If the occiput was originally directed toward the left  it rotates toward the left ischial tuberosity

42. Expulsion • After delivery of the shoulders, the rest of the left body is quickly extruded

47. Changes in shape of the fetal head 1. Caput Succedaneum • The formation of swelling due to stagnation of fluid in the layers of the scalp beneath the girdle of contact • The girdle of contact is either : • Bony • Dilating cervix • Vulval ring

48. The swelling : • Diffuse • Boggy • Not limited by the suture line • Disappears spontaneously within 24 hours after birth • Occurs after rupture of the membranes

49. Importance • It signifies static position of the head for a long period of time • Location of the caput  gives an idea about the position of the head occupied in the pelvis and the degree of flexion achieved : • in left position  caput in right parietal bone • in right position  on left parietal bone • With the increasing flexion  the caput is placed more posteriorly