Normal Labor or Delivery

1. Normal Labor or Delivery Chen Danqing Women’s hospital,School of medicine, Zhejiang University

2. Objective • Definition of labor. • Determinate Factors of Labor • Anatomical considerations: • The female pelvis. • The fetal skull. • The stages of labor. • The mechanism of labor (vertex, LOA). • Management of normal labor.

3. Definitions：Labor is the process by which contractions of the gravid uterus expel the fetus and the other products of conception after 28 weeks from the last menstrual period. It begins when uterine contractions of sufficient intensity, frequency & duration are attained to bring about progressive effacement & dilatation of the cervix as well as descent of the presenting part. Spontaneous or induced Term or preterm

4. Term Delivery：A term delivery occurs between 37 and 42 weeks from the last menstrual period. Premature Delivery：Preterm labor is that occurring before 37 weeks of gestational age. Postdate pregnancy：Postdate pregnancy occurs after 42 weeks .

5. The etiology of labor • These mechanisms are not well defined in humans. • Cervix ripend and lower uterine segment development theory； • Endocrine regulating theory； • Mechanical theory； • Neurohumor theory； • Immunologic theory； Maturation of fetus and change of uterus function is necessary.

6. Four Determinate Factors of Labor The progress and final outcome of labor are influenced by 4 factors . (1)the powers (2)the passage (3)the passenger (4)the psyche

7. The Expulsive Forces(The powers) The power that expulse the fetus and the other products of conception is called the expulsive forces, which include ♀Uterine contraction ♀Intra-abdominal pressure ♀Levator ani muscles contractions.

8. Uterine Contractions Have three unique characteristics: ★Rhythm:increase in frequency and duration,is the important marker of in labor。rhythm ★ Symmetry andpolarity Symmetry and polarity ★ Retraction Retraction

9. Periods of relaxation between contractions are essential to the welfare of the fetus. 极期 进行 退行 宫缩 间歇期 宫缩 Rhythm Increase in frequency and duration

10. The intensity of the upper segment of the uterus is the most strong Symmetry andPolarity

11. The Intra-Abdominal Pressure ＆It is a necessary auxiliary to uterine contractions in second stage of labor. ＆After the placenta has separated, its spontaneous expulsion is aided by the mother increasing intra-abdominal pressure.

12. 腹肌 子宫收缩力 膈肌 肛提肌

13. Levator ani muscles contractions ※ Form a V-shaped sling that tends to rotate the occipital anteriorly(internal rotation). ＆Help the fetus’ extension and delivery. ＆Help the expulsion of the placenta.

14. Passage including: the bony pelvis and soft tissues of pelvis • True vs. false pelvis. • True pelvis: • Pelvic brim. • Pelvic cavity. • Pelvic outlet.

15. bony pelvis 髂 骨 os ilium 骶 骨 Os sacrum 骶 尾 关 节 Sacro-iliac jiont 尾 骨 Os coccyx 耻骨联合 Symphysis publis 坐骨结节 Os ischium

16. Thebony pelvis (the true pelvis) Pelvic inlet plane Pelvic midplane Pelvic outlet plane Three pelvic plane:

17. The Pelvic Inlet • Shape: • Oval & in one plane. • Boundaries: • Anteriorly: SP. • Laterally: upper margin of pubic bone & iliopectineal line. • Posteriorly: sacral promontory. • Dimensions: • AP=11 cm Transverse=13.5 cm.

18. The true conjugate The inclined diameter The transverse diameter

20. Three anteroposterior diameters of the pelvic inlet

21. Pelvic Midplane The smallest plane of the pelvis, particular importance in obstructed labor. Anteroposterior diameter of mid pelvis,average 11.5cm. Transverse diameter of mid pelvis,alse be called interspinous diameter,average 10cm.

22. Anteroposterior diameter of mid pelvis Transverse diameter of mid pelvis

23. Transverse diameter of the midpelvis

24. Pelvic Outlet Plane Four diameters, Anteroposterior, diameter of outlet, 11.5cm。 Transverse outlet, the distance between the inner edges of the ischial tuberosities,9cm Anterior sagittal diameter,6cm Posterior sagittal diameter,8.5cm

25. 1、Transverse outlet 2、 Anterior sagittal diameter 3、 Posterior sagittal diameter 4、 Anteroposterior diameter of outlet 4

27. Pelvic axis and Inclination of pelvic Pelvic axis：The axis of the pelvis refers to the curve of the birth canal as described by a line drawn through the center of each of the four planes. Inclination of pelvic :The angle of the pelvic inlet plane with ground level when women stand.always 60 degree.

28. pelvic axis inclination of pelvic 骨盆轴

31. The Soft Part of the Birth Canal Formation of lower uterine segment,cervix,vagina,soft tissue in the floor of pelvis.

32. The Lower uterine segment Developed from the isthmus of the uterus of nonpregnant women. Physiologic retraction ring : The actively contracting upper segment becomes thicker as labor advances,the lower uterine segment is relatively thin compared with the upper segment,between them a physiologic retraction ring appear.

34. Changes of cervix Effacement of cervix The upper segment contracts, retracts, and expels the fetus; in response to the force of the contractions of the upper segment, the ripened lower uterine segment and effacement of cervix.

36. Dilatation of Cervix In response to the force of the contractions of the upper segment, effacement of cervix and dilatation, through which the fetus can be extruded.

37. Change of cervix during labor Effacement of cervix dilatation of cervix primigravida multipara

38. A crook canal formed by the vagina、tissue of pelvic floor and perineum as the fetal descending.

39. Passenger Fetus(weight,position,presentation, malformation) Fetal weight, 2500g - <4000g Fetal lie, the relation of the fetal long axis to that of the mother. Fetal presentation, the presenting part is either foremost within the birth canal or in closest proximity to it.LOA LOP LOT ROA ROP ROT

40. Size of the fetus head Very important for delivery。 The vault is composed of 2 frontal bones,2 parietal bones, 2 temporal bone and one occipital bone. They are slightly separated from one another at the margins of abutment and by wider spaces, the anterior and posterior fontanelles.

41. Four diameter of fetus head： Biparietal diameter,The greatest transverse diameter of the head,which extends from one parietal bone to other. Average 9.3cm. Occipito-frontal diameter：Which follows a line extending from a point just above the root of the nose prominent portion of the occipital bone. Average 11.3cm.

42. Suboccipito-bregmatic diameter. Which follows a line drawn from the middle of the large fontanel to the undersurface of the occipital bone just where it joins the neck. Average 9.5cm Occipito-mental diameter：From the chin to the most prominent portion of the occiput. Average 13.3cm

43. Suboccipito-bregmatic occipito-frontal Occipito-mental diameter

45. Position of the fetus Fetal position of a particular presentation refers to the relationship of an arbitrary reference point on the fetus to a specific point in the right or left side of the maternal pelvis.

46. Psychologic Factors A high level of anxiety during pregnancy has been associated with decreased uterine activity and with longer and dysfunctional labor。

47. Mechanism of Labor • Mechanism of normal labor in occiput presentation include these cardinal movements of labor. • engagement • descent • flexion • internal rotation • Extension • external rotation,and expulsion.

48. Engagement The mechanism by which the biparietal diameter,the greatest transverse diameter of the fetal head in occiput presentations,passes through the pelvic inlet is defined engagement.

49. Descent Descent continues progressively until the fetus is delivered;the other movements are superimposed on it.

50. Flexion In flexion,the chin is brought into more intimate contact with the fetal thorax,and the appreciably shorter suboccipitobregmatic diameter(9.5cm) is substituted for the longer occipitofrontal diameter(11.3cm).