Factors affecting Labor

The 5(3) Ps)

• Passenger (fetus & placent)

• Passageway (birth canal)

• Powers (contractions)

What’s included in passenger?

• Fetal presentation

• Fetal lie

• Fetal attitude

• Fetal position

• Station

• Engagement

What is fetal presentation?

• Part of the fetus that enters the pelvic inlet first

• Part of the fetus that lies closest to the internal os of cervix (cephalic/occiput, breech/sacrum, shoulder/scapula)

• When the presenting part is occiput, the presentation is a VERTEX (head-first)

What is fetal lie?

Long axis (spine) of the fetus in relation to the long axis (spine) of patient

• Longitudinal/parallel is a cephalic or breech presenation

• Vaginal birth CANNOT occur when the fetus is in transverse/latitude lie

What is fetal attitude?

Posture of the fetus in relation to fetal parts to one another

• Noted by flexion/extension of fetal joints

How does the fetus maintain its posture?

By its mode of fetal growth; it conforms to the shape of the uterus

What can abnormal attitude result in?

Difficulties during childbirth

• Prolonged labor

• Instrumental deliveries

What is biparietal diameter?

The largest transverse measurement (9.25cm); indicator of head size

Fetal position

The relationship of a reference point on the presenting part (occiput, sacrum, mentum, sinciput) to the four quadrants of the mother’s pelvis (ex: ROA, LOA, ROP, LOP)

Station

The relationship of the presenting fetal part to an imaginary line drawn between the ischial spines of the pelvis

• a MEASURE of the degree of descent of the presenting part of the fetus through the birth canal

• Birth is IMMINENT (born NOW) when the presenting part’s station is +4 or +5

• Should be determined when labor begins

Engagement

The largest transverse diameter of the presenting part (ex: BPD went through the pelvic inlet and into the pelvis; station is now at zero)

• Often occurs weeks before labor begins in nulliparas/before or during labor in multiparas

• Can be determined by abdominal or vaginal examination

What are primary powers responsible for?

• INVOLUNTARY

• Contractions (frequency, duration, intensity)

• Move downwards over the uterus in waves, separated by short rest periods

• Responsible for effacement (cervix thinning), dilation, & descent of the fetus

Effacement definition?

Shortening and thinning of the cervix during the 1st stage of labor

• Signals the beginning of labor

What are secondary powers responsible for?

• Bearing down powers (when cervix is fully dilated (100% complete)

• NO effect on cervical dilation

• Occurs when presenting part reaches pelvic floor

• Contractions expulsive in nature

• Quality of how the woman pushes (pushing technique)

• ENHANCES THE FORCE OF THE INVOLUNTARY CTX

What exactly are bearing down powers?

When the cervix is fully dilated 100%

• Increased intraabdominal pressure on all sides of the uterus that adds power to abdominal forces

The 4 types of the bony pelvis? (general)

• Gynecoid

• Android

• Anthropoid

• Platypelloid

Assessment for the bony pelvis

Can be performed during the 1st prenatal evaluation and doesn’t need to be repeated if the pelvis is adequate size and shape

What is unique about the gynecoid bony pelvis?

MOST ideal for child-bearing.

• Wide & round

• Gives room for the fetus to rotate & descend smoothly through the birth canal

Bony pelvis anatomical structure

• Ileum

• Ischium

• pubis

• Sacrum

• Coccyx

What 2 parts is the bony pelvis made of?

• False pelvis

• True pelvis

What is the true pelvis?

Lower part of the pelvis

• Includes the inlet, mid-pelvis, outlet

• Plays a part in childbearing

What are the signs preceding labor?

• Lightening/dropping

• Lower back pain

• Possible rupture of membranes

• Return of urinary frequency

• Stronger BRaxton Hicks contractions

• Weight loss of 0.5-1.5 (approx. 1-3.5lb)

• Surge of energy

• Increased vaginal discharge, bloody show

• Cervical ripening

• Possible rupture of membranes

Mechanisms of labor

• Engagement

• Descent

• Flexion

• Internal rotation

• Extension

• Restitution

• External rotation

• Expulsion

Engagement

The greatest diameter of the fetal head passes through pelvic inlet

Descent

When the fetus moves through the birth canal during the first and second stage

• Measured by station of presenting part

Flexion

Chin of the fetus moves toward the chest; occurs when descending head meets resistance from maternal tissues

• Allows smaller diameter to present to outlet

Internal rotation

The fetal head must internally rotate to exit the outlet, which is widest in the anteroposterior (AP) diameter.

Extension

Occiput passes under lower border of symphysis pubis; occiput is seen, then face followed by chin emerge from the vagina

• Begins at ischial spines, does not complete until presenting part reaches lower pelvis

Restiution

Following delivery of the head, the shoulders rotate briefly

External rotation

During this movement, the shoulders align in the ap diameter.

Expulsion

When the anterior shoulder comes first followed by the remainder of the body

• head & shoulders are lifted up toward the mother’s pubic bone