Physiological Adaptations to Labor and Delivery
Labor - the process by which the products of conception are expelled from
the body.
Delivery - refers to the actual birth
Essential Factors in Labor
Successful labor and delivery results from the effective interplay of several factors:
anatomic, physiologic, and physiological. These factors are referred to as the four
“P”s: Passenger, Passageway, Powers and the Psychological.
The Birth Passage:
Pelvis -the purpose of examination of the bony pelvis is to determine if the
pelvic cavity is of adequate size to allow for the passage of the full term infant.
True pelvis and false pelvis:
a. False pelvis supports weight of uterus. Shallow basin
above the inlet or brim.
b. True pelvis consists of brim or inlet - upper margin pubic
bone posteriorly by upper margin of sacrum. Outlet pubic arch to tip of coccyx.
Types of pelvis - the most satisfactory for delivery is gynecoid. (anthropoid,
android, plattypoid)
The portion of the pelvis that has the most impact on a successful labor and
delivery is the outlet. If the baby enters the inlet and progresses down the
birth canal and cannot get through the outlet, then there are problems.
The Passenger / the Fetus
1.
Fetal Head - because of its size and rigidity, the fetal head has a major effect
on the birth process. Looking from the vertex position. Bones - 2 parietal, 2
temporal, 2 frontal, occiput.
These bones are united by sutures, sagittal, lambdoidal, coronal. At
intersections are the anterior fontanel (diamond shaped) and the posterior
fontanel (triangle shaped)
These bones are not firmly united - slight overlapping or molding of head
occurs in labor. Slide over one another permits adaption. Head can also
rotate, flex, and extend.
Measure head to check if can fit through pelvis. Bi-parietal diameter and bitemporal diameter are measured.
2.
Fetal Lie - relationship of long axis of fetus to long axis of mother.
a. Longitudinal lie - parallel with each other cephalic or breech, optimal
b. Transverse lie - across axis, usually have C-section
3. Attitude - relationship of fetal body parts to each other. Posture in utero =
ovoid. Head flexed on chest, knees flexed etc. Change in attitude, particularly
the head causes the fetus to present larger diameters of the head to the
pelvis.
4. Presentation - that portion of the fetus that enters the pelvis first and
covers the internal os. The three main types include:
a. cephalic – 95% are in the cephalic presentation. Head presentations are in
three types using the reference point = occiput
1) vertex
2) face
3) brow
4) military
b. breech – 3% are buttocks present first. The reference point = sacrum
c. shoulder –2% are transverse
5.
Position - relationship of the fetal presenting part to the maternal bony pelvis.
The landmark on fetus is the posterior fontanel.
a. Step 1 - determine presenting part. Is it vertex = occiput; face - mentum;
breech = sacrum
b. Step 2 - mothers pelvis is divided into four imaginary quadrants: right or
left; anterior or posterior.
The Passageway
Pelvis -the purpose of examination of the bony pelvis is to determine if the
pelvic cavity is of adequate size to allow for the passage of the full term infant.
True pelvis and false pelvis:
a. False pelvis supports weight of uterus. Shallow basin
above the inlet or brim.
b. True pelvis consists of brim or inlet - upper margin pubic
bone posteriorly by upper margin of sacrum. Outlet pubic arch to tip of coccyx.
Types of pelvis - the most satisfactory for delivery is gynecoid. (anthropoid,
android, plattypoid)
Relationship of Maternal Pelvis and Presenting Part:
Engagement -the largest diameter of the presenting part has passed through the
pelvic inlet. Once this happens you’ve established that the inlet is adequate.
No info about outlet.
The process of Engagement is includes floating or ballotable, dipping, and
engaged.
Station - degree to which the presenting part has descended into the pelvis.
Relationship between the presenting part and the ischial spines. 0 station is
at level of the ischial spines. 0 station is at level of the ischial spines and is
said to be engaged. Above the ischial spines is - (minus) station and below
the ischial spines is + (plus) station.
Primary Forces of Labor - The Powers
Primary Powers:
Involuntary Uterine Contractions - muscular contractions effect all the
changes during the first stage of labor which lead to complete dilation and
effacement of the cervix.
Secondary Powers:
Voluntary Uterine Contractions - abdominal muscles assist in second stage
with pushing. Bearing down urge results in upper intra-abdominal pressure
that compresses all sides of uterus and aids in expulsive forces.
Psychological Considerations:
Women who are relaxed, knowledgeable of birth process can have an easier
labor. Childbirth classes focus on this concept - decrease fear, decrease tension,
and therefore, decrease pain.
Techniques for Assessment of Labor
Now that we have gone through the four essential factors of labor we are ready to
assess the patient.
I.
Abdominal Palpation / Leopold’s Maneuver
The Leopold’s Maneuver is a systematic external examination of the abdomen to
assess fetal position, lie, presentation, fetal movement, number of fetus, and
engagement.
Preparation - empty bladder, lie on back with pillow to tilt to side, knees flexed to
relax abdomen.
Procedure -stand on right side face woman and begin. Palpate with fingers and
palms of hands, not fingertips.
1. Start at upper fundus, palpate for head or buttocks
2. With palms go down each side and locate back
3. Gently grasp lower portion with thumb and forefinger and feel for the
head
4. Turn and face woman=s feet and repeat the procedure
Auscultation
Assess for the area of greatest intensity of the FHR. Can determine if breech
or vertex and right or left.
Vaginal Examination
Sterile examination per vagina to determine:
1.
Presentation
2.
Position - find sagittal suture and fontanels, usually the posterior fontanel
3.
Condition of Membranes - intact or bulging. If think may be ruptured then
check with nitrazine paper -will turn blue. Then perform fern test.
4.
Effacement -shortening and thinning of cervix. The cervix is obliterated or
taken-up by shortening of the uterine muscles. Pulled into the lower uterine
segment. Measured in % ranging from 0%-100%.
5.
Dilatation -Enlargement and widening of cervical os. Dilatation of cervix is
involuntary and occurs by the drawing upward of the musculofiber
components of the cervix. Measure in cm. 0-10 cm. Dilatation of cervix is
the result of: contractions; pressure of amniotic fluid sac; and pressure of the
presenting part.
6.
Station – where is the presenting part – at 0 station is at level of the ischial
spines and is said to be engaged, above the ischial spines is - (minus) station,
or below the ischial spines is + (plus) station.
7.
Engagement –is the fetus ballottable, dipping, or engaged.
Ultrasound
Passage of high-frequency sound waves through uterine area to determine
pelvic measurements, locate placenta, and observe fetal outline.
Physiology of Labor
Causes of Labor:
The cause of onset of labor is unknown. Many theories have been said to explain
why. Probably the result of a combination of several factors.
1. Progesterone withdrawal hypothesis - A decrease in level of progesterone.
Estrogen levels can rise with the decrease in progesterone.
2. Prostaglandin Hypothesis -high level of prostaglandins trigger contractions
3. Corticotropin-releasing hormone – CRH levels rise at pregnancy term
Premonitory Signs and Symptoms of Labor:
Premonitory signs or impending signs are the physiological changes that take place
the last several weeks of pregnancy or even the last several hours.
1.
Lightening - descent of uterus downward and forward B the presenting part
descends into the pelvis. Found on office visit when measure fundus it
decreases. Woman can breathe easier, but feels pelvic pressure, leg cramps,
and need to void.
2.
False labor pains increase - Braxton-Hicks may become painful and similar
to true labor. Usually felt in abdomen and cervix does not dilate and efface.
3.
Show - expulsion of mucus plug -pinkish to blood tinged. Labor usually
begins in 24-28 hours after expelled.
4.
ROM varies from trickle (may think have urinary incontinence) to gush of
amniotic fluid. No such thing as dry labor - amniotic fluid produced until
delivery. Check with nitrazine paper.
5.
Backache – usually occurs day before going into labor
6.
Diarrhea
7.
Sudden increase in energy – nesting instinct
True Labor vs. False Labor:
True Labor
False Labor
Contractions
Regular, increase in
intensity with walking;
increase in frequency and
duration
Irregular, intensity
unchanged
Discomfort
Lower back and radiates
girdle-like fashion from
back to front of abdomen
Abdomen or groin relief
with walk
Cervix Show
Progressively D & E.
pinkish
No change; none, or
brownish; if had vaginal
exam in last 48 hours
Phases and Stages of Labor:
Stage I
Phase I
Phase II
Phase III
Stage II
0-10 cm
Early or latent phase 0-3 cm
Mid-phase or active phase 4-7 cm
Transition phase 8-10 cm
Birth of Baby / pushing stage
Stage III
Stage IV
Birth of Placenta
Recover 1-2 hours post-partum
Forces of Labor:
 Contractions - each contraction exhibits a wavelike pattern that begins slow
increment, reaches acme (peak), and then diminishes (decrement). As
labor progresses, contractions should increase in discomfort, intensity, and
duration.
 Frequency - beginning of the increment of one contraction to the beginning
of the increment of the next contraction.
 Duration -beginning of the increment to the completion of decrement of the
same contraction.
 Assessment of Contraction - 1) subjective symptom by the woman; 2)
palpation and timing by nurse with fingers placed lightly on the fundus of
the uterus; 3) use of electronic monitoring.
Duration of Labor:
Length
1.
2.
3.
of labor depends on:
Regular progression of labor
Effacement and regular progressive dilation of cervix
Progress in descent of presenting part
4.
Preparation and relaxation of the mother
The length depends on the greater resistance of the cervix.
Primigravida - up to 22 hours. Average = 12. 2 hours
Multigravida - 8-16 hours
Mechanisms of Second Stage:
1.
2.
3.
4.
5.
6.
Descent
Flexion
Internal Rotation
Extension
External Rotation
Expulsion
Placental Separation:
1. Globular rise in the abdomen
2. Sudden gush of blood
3. Lengthening of the umbilical cord