Labor Onset Theories and The Five Ps

Theories Concerning Labor Onset

• A cue from fetal proteins in the lungs may play a significant role in initiating labor.

Impending Signs and Symptoms of Labor

• Braxton Hicks contractions
• Bloody show
• Lightening
• Nesting
• Cervical changes
• GI symptoms
• Weight loss

The Five Ps

• Power: The force that moves the fetus through the maternal pelvis
  • Primary power: Involuntary uterine contractions and the Ferguson reflex (reflex to push)
  • Secondary power: Voluntary pushing
• Passageway: Anatomy of the bony pelvis and soft tissues
  • True pelvis is the most important, consisting of the inlet, midpelvis, and outlet.
  • Softening of cartilage due to increased relaxin levels.
• Passenger: The fetus
  • Fetal head: Size and molding
  • Fetal presentation: Part entering the pelvis first (cephalic, breech, or shoulder)
  • Fetal attitude: Relationship of fetal body parts to each other (vertex, sinciput, brow, facial)
  • Fetal lie: Relation of maternal spine to fetal spine (longitudinal or transverse)
  • Fetal position: Relationship of the presenting part to the maternal pelvis (described with a 3-letter abbreviation: L or R, O, M, Sc, S, P, A, T)
• Psyche: Psychological factors
  • Anxiety, culture, expectations, life experiences, and support affect response to labor and birth.
• Position: The laboring woman's posture
  • Upright positions may result improved outcomes: decreased Cesarean section, surgical vaginal birth, episiotomy, and spontaneous lacerations; shorter first and second stages; and increased maternal control and comfort.

True vs. False Labor

• 4-1-1 Rule: Contractions are 4 minutes apart, last for 1 minute, for 1 hour.

Labor Progression: Cervix

• Dilation: The drawing up and opening of the cervix (ranges from fully closed to 10 cm)
• Effacement: The thinning and shortening of the cervix (expressed as a percentage)

Labor Progression: Station

• Describes the descent of the presenting part through the true pelvis using the ischial spines as reference.
  • Level of ischial spines is Zero and means the part is “engaged”
  • Negative numbers mean the presenting part is still “floating” and not engaged
  • When the presenting part moves beyond the ischial spines, it has a positive number (+1 to +3, with +3 being the most descended).

Cardinal Movements of Labor

• Engagement: Head reaches the ischial spines.
• Descent: Fetus moves past “0” (pt typically feels Ferguson reflex [urge to push] at +1).
• Flexion: Fetal head moves chin to chest, causing biparietal diameter to be the widest dimension of the presenting part.
• Internal Rotation: Fetal head rotates to align the widest part with the widest part of the pelvic cavity.
• Extension: Fetal chin comes off chest and neck arches as it is born.
• External Rotation (restitution): Fetal head, now born, rotates to align with the shoulders.

Stages of Labor

• First Stage: Cervical dilation and effacement occur.
  • Latent Phase: Cervix dilation 0-3 cm
  • Active Phase: Cervix dilation 4-7 cm
  • Transition Phase: Cervix dilation 8-10 cm
• Second Stage: The expulsion stage, begins with full dilation and effacement of the cervix and ends with the birth of the baby.
• Third Stage: Begins with the birth of the baby and ends with the expulsion of the placenta.
• Fourth Stage: The stage of physical recovery for mother and infant, begins with the delivery of the placenta and lasts 1-4 hours after birth.

Initial Admission Assessment of Labor

• Maternal vital signs: HR, Temp, RR, O2 saturation, Blood Pressure, Pain scale
• External Uterine Toco and External Fetal Heart Rate Monitor (FHR): Uterine toco placed at the top of the fundus and midline, firmly in place; external FHR monitor placed by the fetal back using Leopold’s maneuvers.

Hemorrhage Risk Assessment

• All women in labor and delivery should be assessed for hemorrhage risk on admission, 30-60 minutes before birth, and 30-60 minutes after birth.
• Categories of Risk:
  • Low Risk: Draw blood and hold specimen
  • Moderate Risk: Draw and send Type and Screen and Review Hemorrhage Protocol.
  • High Risk: Type and Cross match for 2 units PRBC’s, Review Hemorrhage Protocol, Team Prebrief.

Stage 1: Latent Phase

• Historically 0-3 cm (recent research suggests it can last up to 6 cm)
• Length varies (typically longer for nulliparous than multiparous)
• May report cramping-like sensations similar to menstrual cramps; often able to talk through the contractions.
• Admission to the hospital in the absence of maternal and fetal complications is not ideal during this phase.
• "Six is the new Four": Delay admission until 6 cm dilated?
• Encourage walking, showering, light snacking, and hydration.

Stage 1: Active Phase

• Dilation between 4-7 cm
• Fetus descends into the pelvis, and internal rotation begins.
• Multiparous woman should have cervical change of 1.5 cm/hr and nulliparous woman 1.2 cm/hr.
• Known as the Friedman’s curve and is an approximation.
• Contractions are 3-5 minutes apart with a duration of 30-45 seconds and are moderate to strong intensity.
• Optimal time for an epidural block.
• Behavior changes include anxiety, helplessness, intense focus throughout the contraction, and an inability to engage socially as she is concentrating very hard on her task at hand.
• Treatment with Ibuprofen and ice packs.