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 contractions1. Result in progressive

cervical dilation and

effacement.

Do not result in progressive

cervical dilation and

effacement.2. Occur at regular

intervals.

Occur at irregular intervals.

3. Intervals between

contractions decrease.

Intervals remain the same or

increase.4. Intensity increases. Intensity decrease or

remains the same. 5. Location mainly in back

and abdomen.

Location mainly in groin

and abdomen.6. Generally intensified by

walking.

Generally unaffected by

walking.

7. Not affected by mild

sedation.

Generally relived by mild

sedation. 8. Dilation and effacement

of the cervix are

progressive.

There is no change in the cervix.

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 4-

7 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.