Normal labor
Labor is described as the process by which the fetus,
placenta and membranes are expelled through the birth
canal. Normal labor occurs at term and is spontaneous in
onset with the fetus presenting by the vertex. The process
is completed within 18 hours and no complications arise.
Initiation of labor:
The exact mechanism that initiates labor is unknown.
Theories include the following:
1. Uterine stretch theory:
uterus becomes stretched,
pressure increase causing physiologic changes that
initiate labor. stretching causes a release of
prostaglandins.
2. As pregnancy advances, the uterus becomes more
sensitive to oxytocin (pressure on cervix stimulate
production of oxytocin).
3. As pregnancy advances, progesterone is less effective
in controlling rhythmic uterine contractions that
occur normally throughout pregnancy.
4. There is increased production of prostaglandins by
fetal membranes and uterine deciduas as pregnancy
advances.
5. In later pregnancy, the fetus produces increased
levels of cortisone which inhibit progesterone
production from the placenta.
6. Placental aging and deterioration triggers the
initiation of contractions.
General terms:
1. Lie: a comparison of the long axis of the fetus with
the long axis of the mother.
Fetal lie is either,
longitudinal, transverse or oblique. In longitudinal lie
either the fetal head presents or the buttocks present.
In transverse lie, the shoulders present.
2. Presentation: the part of the fetus deepest in the
birth canal. Presentation may be vertex, face, brow,
breech or shoulder.
3. Presenting part: portion of the fetus deepest in the
birth canal and felt on vaginal examination.
4. Attitude:
relationship of fetal parts to each other
(normal flexion).
5. Position: Position refers to the location of a fixed
reference point on the fetal presenting part in relation
to a specific quadrant of the maternal pelvis. The
presenting part can be right anterior, left anterior,
right posterior, and left posterior. These four
quadrants designate whether the presenting part is
directed toward the front, back, right, or left of the
passageway.
It is the relationship of landmark on the fetal
presenting part to the front (anterior = A) back
(posterior = P) or side (transverse = T) of the mothers
pelvis.
Landmarks on the fetal presenting parts
include head = occiput (O) buttocks = sacrum (S),
shoulder = scapula or acromion (A), face = chin of
mentum (M).
Example: a fetus presenting by the vertex with his occipit
on the left anterior part of the woman’s pelvis would have
his presentation and position described as LOA or lift
occiput anterior.
Factors affecting labor:
• Powers (physiological forces)
• Passageway (maternal pelvis)
• Passenger (fetus and placenta)
• Passageway _ Passenger and their relationship
(engagement, attitude, position)
• Psychosocial influences (previous experiences,
emotional status)
Successful labor and delivery depend on adequate pelvic
dimensions, adequate fetal dimensions, presentation and
adequate uterine contractions.
A.
Pelvic dimensions:
1. Adequate pelvic inlet. AP diameter, normal shape.
2. Adequate midpelvis: Ischia spines don’t protrude
into bony canal.
3. Adequate outlet:
adequate distance between
tubrosities and coccyx.
B.
Fetal dimensions:
Important fetal dimensions influenced by fetal size,
posture, lie, and presentation. Fetal position is also
an important factor in successful labor.
C.
Uterine contractions:
1. Uterine contractions are involuntary, occurring at
regular intervals and having adequate intensity.
2. During uterine contractions, the active upper
portion becomes thicker, while the lower uterine
segment stretches and becomes thinner.
True and false labor contractions
True labor contractions
false labor contractions
1. Result in progressive Do not result in progressive
cervical
dilation
and cervical
effacement.
2. Occur
at
dilation
and
effacement.
regular Occur at irregular intervals.
intervals.
3. Intervals
between Intervals remain the same or
contractions decrease.
4. Intensity increases.
increase.
Intensity
decrease
or
remains the same.
5. Location mainly in back Location mainly in groin
and abdomen.
and abdomen.
6. Generally intensified by Generally
walking.
walking.
unaffected
by
7. Not affected by mild Generally relived by mild
sedation.
sedation.
8. Dilation and effacement There is no change in the
cervix.
of the cervix are
progressive.
 Events preliminary to labor (Signs and symptoms of
labor):
Pre-labor is the term given to the last few weeks of
pregnancy during which time a number of changes
occurring.
1. Lightening, the setting of the fetus in the lower
uterine segment occurs 2-3 weeks before the onset of
labor (38th) in the primigravida and later during labor
in the multigravida.
a. The woman’s breathing becomes easier as the fetus
falls away from the diaphragm.
b. Lordosis of the spine is increased, walking is more
difficult because the pelvic joints are more mobile
and relaxed, leg cramping may increase. Backache
may increase.
c. Frequency of micturation occurs because of the
pressure on the bladder.
2. Vaginal secretions may increase.
3. Mucus plug is discharged from the cervix along with
a
small
amount
of
blood
from
surrounding
capillaries, referred as SHOW (bloody show). Its
presence often indicates that labor will begin within
24 to 48 hours.
4. Taking up of the cervix.
The cervix softens
(“cervical ripening”), stretches, and thins, and
eventually is taken up into the lower segment of the
uterus. This softening and thinning is called cervical
effacement
5. False labor contractions; Braxton-Hicks contractions
may occur q 10-20 minutes.
6. Membranes may rupture, only 12% have spontaneous
ROM, otherwise amniotomy.
7. In addition to some other signs; energy spurt, wt loss
(.5-1.5kg due to fluid loss), and GI disturbance.
Stages of labor
1. The 1st stage is that of dilation of the cervix.
It
begins with regular rhythmic contractions and is
complete when the cervix is fully dilated 10 cm
(takes most of the time). It consists of 3 phases;
latent, active, and transition.
2. The 2nd stage of labor is the expulsion of the fetus. It
begins when the cervix is fully dilated and is
completed when the baby is completely born.
3. The 3rd stage of labor includes separation and
expulsion of placenta and membranes. It lasts from
the birth of the baby until the placenta and the
membranes have been expelled. (about half an hour)
4. The 4th stage lasts from delivery of the placenta until
the postpartum condition of the woman has become
stabilized “usually 1-2 hour after delivery”
 Note: the 1st stage consists of 3 phases:
a. Latent phase: cervical dilation is 0-3 cm
Begins with the establishment of regular contractions
(labor pains). Labor pains are often initially felt as
sensations similar to painful menstrual cramping and
are usually accompanied by low back pain.
Contractions during this phase are typically about 5
minutes apart, last 30 to 45 seconds, and are
considered to be mild. Usually, woman is excited
about labor and chatty. It takes up to 10-14 hours.
b. The active phase of labor; a cervical dilation is 47 cm. It is characterized by more active
contractions. The contractions become more
frequent (every 3 to 5 minutes), last longer (60
seconds), and are of a moderate to strong intensity.
Cervical dilation during this phase advances more
quickly as the contractions are often more efficient.
While the length of the active phase is variable,
nulliparous women generally progress at an average
speed of 1 cm of dilation per hour and multiparas at
1.5 cm of cervical dilation per hour.
c. Transitional phase: cervical dilation is 7-10 cm
The transition phase is the most intense phase of
labor. Transition is characterized by frequent, strong
contractions that occur every 2 to 3 minutes and last
60 to 90 seconds on average.
Other sensations that a woman may feel during
transition include rectal pressure, an increased urge to
bear down, an increase in bloody show, and
spontaneous rupture of the membranes (if they have
not already ruptured).
Mechanism of labor
If the woman’s pelvis is adequate, size and position
of the fetus are adequate and uterine contractions are
regular and of adequate intensity, the fetus will move
through the birth canal.
The position and rotational
changes of the fetus as he/she moves down the birth canal
will be affected by resistance offered by the woman’s
bony pelvis, cervix and surrounding tissues
A.
Engagement:
When biparietal diameter of fetal head has passed through
pelvic inlet.
1. Primigravida: occurs up to 2 weeks before onset of
labor
2. Multigravida: usually occurs with onset of labor.
3. Since biparietal diameter of fetal head and AP
diameter is narrowest of pelvic inlet, the fetal head
usually enters pelvis in a transverse position.
The fetal head enters the maternal inlet in the occiput
transverse or the oblique position because the pelvic
inlet is widest from side to side.
B.
Descent:
Occurs throughout labor and is essential for rotations of
the fetus prior to birth:
1. Accomplished by force of uterine contractions on
fetal portion in funds, during second stage of labor
the bearing down increases intra-abdominal pressure
thus augmenting effects of uterine contractions.
2. Degree of descent described as:
a. Floating: presenting part is not engaged in pelvic
inlet.
b. Fixed presenting part has entered pelvis
c. Engagement: presenting part has passed pelvic
inlet
d. Station O: presenting part has reached the level of
ischial spine
e. Stations (-1,-2,-3,-4) presenting part in 1,2,3,4 cm
above the level of ischial spine.
f. Stations (+1, +2, +3, +4) presenting part in 1, 2, 3,
4 cm below the level of ischial spine. A station of
+4 indicates that presenting part is on pelvic floor.
C.
Flexion
Resistance to descent causes head to flex so that the chin
is close to the chest. This cause the smallest fetal head
diameter, subocciputobregmatic (9.5 cm) to present
through the canal.
D.
Internal rotation:
In accommodating to the birth canal, the fetal occiput
rotates interiorly from its original position toward the
symphysis pubis.
E.
Extension:
As the fetal head descends further, it meets resistance
from the perineal muscles and is forced to extend. The
fetal head becomes visible at the vulvovaginal ring. Its
largest diameter is encircled (crowing) and the head then
emerges from the vagina.
The head is born in extension as the occiput slides under
the symphysis and the face is directed toward the rectum.
The fetal brow, nose, and chin then emerge.
F. External rotation:
When the head emerged, the shoulder are undergoing
internal rotation to accommodate to the birth canal, the
head now born, rotates as the shoulders undergo the
internal rotation.
G.
Expulsion
Following delivery of the infant’s head and internal
rotation of the shoulder, the anterior shoulder rest beneath
the symphonies pubis. The posterior shoulder is born
followed by the anterior shoulder and the rest o the body.