The course and conduct of normal labor and delivery Song Weiwei OB&GY Department of Shengjing Hospital. Definition of labor. Labor is strictly defined as regular uterine contractions with resultant change of cervical effacement and dilatation and extrusion of the products conception.
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The course and conduct of normal labor and deliverySong WeiweiOB&GY Department of Shengjing Hospital
Labor is strictly defined as regular uterine contractions with resultant change of cervical effacement and dilatation and extrusion of the products conception.
No exact course has been found that can initiate the onset of labor.
Four factors that determine
a normal labor
(3 Ps: powers, passage and passenger)
----- uterine contraction
Characteristics of uterine contraction
pelvis: size \shape\ inclination of pelvis
vagina、cervix、low segment of uterine
cervical effacement :2~3cm before labor
cervical dilatation: closed to 10cm open
Lie- relationship between the long axis of the fetus and that of the mother (longitudinal, transverse or oblique).
Presentation- the fetal part that lies closest to the pelvic inlet (cephalic - vertex, face; breech; shoulder).
Position- relationship of the fetal parts to maternal parts.
Body weight of fetus
Diameters of fetal skull
latent phase: in which early cervical effacement and dilation occur:0~3cm.
active phase: cervical dilation becomes more rapid (approximately 3 to 4 cm to full dilation of 10cm).
The special labor mechanisms is due to asymmetry of the shape of both the fetal head and maternal pelvis.
Changes in the position of the fetal head are required for the average size fetus to accomplish passage through the birth canal.
The rotations are accomplished by the propulsive force of uterine activity.
2. internal rotation
4. external rotation
movements of the head
It is the descent of the largest transverse diameter of fetal head (BPD) to a level below the plane of the pelvic inlet.
Then the head is engaged.
Flexion (I movement of the head)- placement of the fetal chin on the thorax (fetus takes a chin-to-chest posture)
Internal rotation (II movement)- the occiput rotates toward the mother’s pubic symphysis.
Begins at the level of maternal vulva
The fetal head is delivered by extension from the flexed to the extended position rotating around the symphysis pubis ( the occiput arches toward the fetal back).
After delivery of the head the forces exerted on the head by the maternal pelvic musculature are relived and the fetus resumes its normal face-forward position.
Its face begins to „look” at one of mother’s leg.
Delivery of the shoulders - first the anterior one (under the symphysis pubis) and then the posterior one.
The rest of the body is usually quickly delivered.