Physiology of Normal Labor and Delivery: Part I and II
Neil K. Kochenour, MD
Department of OB/GYN
U of U College of Medicine
Take Home Points
1. To understand and recognize a normal labor pattern.
2. To understand the mechanism of labor for a cephalic presentation.
3. To understand the meaning of the following germs: Presentation, position, lie, station, effacement, dilatation.
4. To understand the phases and stages of labor.
5. To understand the following abnormalities of labor:
Prolonged latent phase,
arrest of dilatation,
and arrest of descent.
6. To understand the indications for cesarean delivery.
7. To understand the indications for forceps delivery.
Attitude: This refers to the posturing of the joints and relation of fetal parts to one another. The normal fetal attitude when labor begins is with all joints in flexion.
Lie: This refers to the longitudinal axis of the fetus in relation to the mother’s longitudinal axis (i.e., transverse, oblique, or longitudinal (parallel).
Presentations: This describes the part on the fetus lying over the inlet of the pelvic or at the cervical os.
Point of Reference of Direction: This is an arbitrary point on the presenting part used to orient it to the maternal pelvis [usually occiput, mentum (chin) or sacrum].
Position: This describes the relation of the point of reference to one of the eight octanes of the pelvic inlet (e.g., LOT: the occiput is transverse and to the left).
Engagement: This occurs when the biparietal diameter is at or below the inlet of the true pelvis.
Station: This references the presenting part to the level of the ischial spines measured in plus or minus centimeters.
Flexion and Engagement: This occurs at various times before the forces of labor begin.
Descent: This occurs as a result of active forces of labor.
Internal Rotation: This occurs as a result of impingement of the presenting part on the bony and soft tissues of the pelvis.
Extension: This is the mechanism by which the head normally negotiates the pelvic curve.
External Rotation(Restitution): This is the spontaneous realignment of the head with the shoulders.
Expulsion: This is anterior and the posterior shoulders, followed by trunk and lower extremities in rapid succession.
1. Characteristics of uterine contractions in labor
2. Mechanisms of labor and delivery
3. Physiology of labor and delivery
4. Forceps delivery
5. Cesarean delivery