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

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.

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

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

Factors Affecting Labor: Passenger (Cont.)

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

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

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

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

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

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

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

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

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

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.

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.

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.

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.

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.

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.