1. Labor and Birth Processes
Chapter 16
Labor and Birth Processes
Copyright © 2016 by Elsevier Inc. All rights reserved.

2. Learning Objectives
Explain the five major factors that affect the labor process.
Describe the anatomic structure of the bony pelvis.
Recognize the normal measurements of the diameters of the pelvic inlet, cavity, and outlet.
Explain the significance of the size and position of the fetal head during labor and birth.
Summarize the cardinal movements of the mechanism of labor for a vertex presentation.
Examine the maternal anatomic and physiologic adaptations to labor.
Describe factors thought to contribute to the onset of labor.
Describe fetal adaptations to labor.

3. Factors Affecting Labor: Passenger
Passenger: fetus
Size of the fetal head
Bones in the fetal skull
Fontanels
Molding
Presentation of the fetus: the part of the fetus that enters the pelvic inlet first and leads through the birth canal during labor
Cephalic
Breech
Shoulder

6. Factors Affecting Labor: Passenger (Cont.)
Passenger: fetus (Cont.)
Fetal lie: the relation of the long axis (spine) of the fetus to the long axis (spine) of the mother
Longitudinal
Vertical
Fetal attitude: the relation of the fetal body parts to one another
General flexion
Critical measurements of fetal head
Biparietal diameter
Suboccipitobregmatic diameter

7. Factors Affecting Labor: Passenger (Cont.)

8. Factors Affecting Labor: Passenger (Cont.)
Passenger: fetus
Fetal position: the relationship of a reference point on the presenting part to the four quadrants of the mother’s pelvis
Position is denoted by a three-part letter abbreviation
Fetal station: a measure of the degree of descent of the presenting part of the fetus through the birth canal
Fetal engagement: usually corresponds to 0 station

10. Factors Affecting Labor: Passageway
Passageway: Birth canal
Bony pelvis: 4 types
Gynecoid
Android
Anthropoid
Platypelloid
Soft tissues

11. Factors Affecting Labor: Powers
Primary powers: contractions
Frequency, duration, intensity
Effacement
Dilation
Ferguson reflex
Secondary powers: bearing-down efforts
Valsalva maneuver

13. Factors Affecting Labor: Position and Psychologic
Position of laboring woman
Discussed in depth in Chapter 19
Psychologic state of laboring woman

14. Process of Labor
Labor: process of moving fetus, placenta, and membranes out of the uterus and through the birth canal
Signs preceding labor
Lightening
Bloody show
Onset of labor
Cannot be ascribed to a single cause

15. Process of Labor (Cont.)
Stages of labor
First stage
Latent phase
Active phase
Transition phase
Second stage
Third stage
Fourth stage

17. Process of Labor (Cont.)
Mechanism of labor
Turns and adjustments necessary in human birth process
Seven cardinal movements of mechanism of labor
Engagement
Descent
Flexion
Internal rotation
Extension
Restitution and external rotation
Expulsion

19. Physiologic Adaptation to Labor
Fetal adaptation
Fetal heart rate (FHR): reliable and predictive information about the condition of the fetus related to oxygenation
Fetal circulation
Fetal respiration

20. Physiologic Adaptation to Labor (Cont.)
Maternal adaptation
Woman exhibits both objective and subjective symptoms
Cardiovascular changes
Respiratory changes
Renal changes
Integumentary changes
Musculoskeletal changes
Neurologic changes
Gastrointestinal changes
Endocrine changes

22. Key Points
Labor and birth are affected by the five Ps: passenger, passageway, powers, position of the woman, and psychologic response.
Because of its size and relative rigidity, the fetal head is a major factor in determining the course of birth.

23. Key Points (Cont.)
The diameters at the plane of the pelvic inlet, the midpelvis, and the outlet plus the axis of the birth canal determine whether vaginal birth is possible and the manner in which the fetus passes down the birth canal.
Involuntary uterine contractions act to expel the fetus and placenta during the first stage of labor; these are augmented by voluntary bearing-down efforts during the second stage.

24. Key Points (Cont.)
The first stage of labor lasts from the time dilation begins to the time when the cervix is fully dilated.
The second stage of labor lasts from the time of full cervical dilation to the birth of the infant.
The third stage of labor lasts from the infant’s birth to the expulsion of the placenta.
The fourth stage of labor begins with the delivery of the placenta and includes at least the first 2 hours after birth.

25. Key Points (Cont.)
The cardinal movements of the mechanism of labor are engagement, descent, flexion, internal rotation, extension, restitution and external rotation, and expulsion of the infant.
Although the events precipitating the onset of labor are unknown, many factors, including changes in the maternal uterus, cervix, and pituitary gland, are thought to be involved.

26. Key Points (Cont.)
A healthy fetus with an adequate uterofetoplacental circulation is able to compensate for the stress of uterine contractions.
As the woman progresses through labor, various body systems adapt to the birth process.

27. Question
With regard to fetal positioning during labor, nurses should be aware that:
Position is a measure of the degree of descent of the presenting part of the fetus through the birth canal.
Birth is imminent when the presenting part is at +4 to +5 cm, below the spine.
The largest transverse diameter of the presenting part is the suboccipitobregmatic diameter.
Engagement is the term used to describe the beginning of labor.
ANS: B
Feedback
A Incorrect: Position is the relation of the presenting part of the fetus to the four quadrants of the mother’s pelvis; station is the measure of degree of descent.
B Correct: The station of the presenting part should be noted at the beginning of labor so that the rate of descent can be determined.
C Incorrect: The largest diameter usually is the biparietal diameter. The suboccipitobregmatic diameter is the smallest, although one of the most critical.
D Incorrect: Engagement often occurs in the weeks just before labor in nulliparas and before or during labor in multiparas.