The Physiology of Labor

Prepared by: Sarah Jane Racal, RN,MAN

Christian University of Thailand

Theories of Labor

1. Uterine Stretch theory -a hollow organ when stretched to capacity contract and empty.

2. Oxytocin theory- production of oxtytocin from posterior pituitary gland----contraction of the uterus.

3. Progesterone Deprivation theory-progesterone inhibit uterine motility. A decrease in progesterone----uterine contraction.

Theories of Labor

4. Prostaglandin Theory- increase prostaglandin synthesis---uterine contraction.

5. Theory of aging placenta- decrease in blood supply to the placenta----uterine contraction.

Premonitory Signs of Labor

1. Lightening2. Braxton Hick’s Contractions3. Sudden burst of maternal energy/activity.4. Slight decrease in maternal weight5. Softening “ripening” of the cervix6. Rupture in the membranes “BOW”7. Show

Premonitory Signs of Labor

1. LighteningThis is the descent/setting of the presenting

part into the pelvic inlet which happens 10-14 days before labor in primigravida and 1 daybefore labor in a multipara. And when the largest diameter of the presenting part passes the pelvic inlet, the head is said to be engaged.

However, lightening is heralded by the following signs:Relief of dyspneaRelief of abdominal tightness

Premonitory signs of labor

1. Lightening

Increased frequency of voiding

Increased amount of vaginal discharge

Increased lordosis as the fetus enters the pelvis and falls further forward

Increased varicosities

Shooting pains down the legs because of pressure on the sciatic nerve

Premonitory signs of labor

2. Braxton Hick’s Contractions-In the last week or days before labor.

These are false labor contractions, painless,irregular,abdominaland relieved by walking, and are also known as practice contractions

Premonitory Signs of Labor

3. A sudden burst of maternal energy/activitybecause of hormone epinephrine. This is meant to prepare the body for the “labor” ahead

Premonitory Signs of Labor

4. Slight decrease is maternal weight.Loss of weight is about 2-3 lbs. One to

two days before the onset of labor because of the decrease in progesterone level and probably loss of appetite.

Premonitory Signs of Labor

5. Softening/”ripening” of the cervix

Goodell’s Sign

Premonitory Signs of Labor

6. Ruptured BOWImportant nursing considerations:A. Ruptured BOWInitial Nursing Action

- Put her immediately in bed and take FHT. Instruct the client not to ambulate---fetal cord compression.

B. Cord ProlapseInitial Nursing Action- Put her on Trendelenburg Position to reduce pressure on the cord.- Remember : only 5 minutes of umbilical cord compression can already

lead to CNS damage and even death.- Apply a warm saline saturated OS on the cord to prevent drying of the

cord.

Premonitory Signs of Labor

7. ShowSudden gush of blood (pinkish vaginal discharge)Nursing Implication:Assess for the color of vaginal discharge* Greenish- meconium stained* Bright Red- vaginal bleeding

Signs of True Labor

1. Uterine ContractionsThe surest sign that labor has begun is the

initiation of effective, productive, involuntary uterine contractions.

There are 3 phases of uterine contractions:• Increment/Crescendo –intensity of the contraction

increases• Apex/Acme –the height or peak of the contraction• Decrement/Decrescendo –intensity of the

contraction decreases

Signs of True Labor

Characteristics of contractions:Frequency of contraction –• this is timed from the beginning of one

contraction to the beginning of the next.Duration of contraction –• this is timed from the moment the uterus first

begins to tighten until it relaxes again.Intensity of contraction –• it may be mild, moderate or strong at its acme.

Mild contraction– the uterine muscle becomes somewhat tense, but can be indented with gentle pressure.

Moderate contraction– the uterus becomes moderately firm and a firmer pressure is needed to indent.

Strong contraction– the uterus becomes so firm that it has the feel of wood like hardness, and at the height of the contraction, the uterus cannot be indented when pressure is applied by the examiner’s hand.

2. Uterine ChangesAs labor contractions progress, the uterus is gradually differentiated into two distinct portions. These are distinguished by a ridge formed in the inner uterine surface, the physiologic retraction ring.

a. Upper uterine segment– this portion becomes thicker andactive, preparing it to exert the strength necessary to expelthe fetus during the expulsion phase.

b. Lower uterine segment– this portion becomes thin-walled,supple, and passive so that the fetus can be pushed cut of theuterus easily.

c. Contour of the uterus changes from a round ovoid to astructure markedly elongated in a vertical diameter thanhorizontally. This serves to straighten the body of the fetusand place it in better alignment to the cervix and pelvis.

3. Cervical ChangesThere are 2 changes that occur in the cervixEffacement

– This is the shortening and thinning of the cervical canal to paper thin edges. To primiparas, effacement is accomplished before dilatation begins while with multiparas, dilatation may proceed before effacement is complete.

Dilatation– This refers to the enlargement of the cervical canal from an opening a few millimeters wide to one large enough (approx. 10 cm) to permit passage of the fetus.

Dilatation occurs for two reasons:

First, uterine contractions gradually increase the diameter of the cervical canal lumen by pulling the cervix up over the presenting part of the fetus.

Second, the fluid-filled membranes press against the cervix.

.4. Show

This is the blood-tinged mucus discharged from the vagina because of pressure of the descending fetal part on the cervical capillaries causing their rupture. Capillary blood mixes mucus when operculum is released.

5. Rupture of the membrane of bag of waters

This is a sudden gush or a scanty slow seeping of amniotic fluid from the vagina. The color of the amniotic fluid should always be noted. At term, this is clear, almost colorless and contains white specks of vernix caseosa.

Green staining means it has been contaminated with meconium. Yellow staining may mean blood incompatibility while pink staining may indicate bleeding.

Once membranes have ruptured, labor is inevitable, meaning to say that uterine contractions will occur within next 24 hours. The initial nursing actions for patients with ruptured membranes are:

• Notify physician• Lie patient to bed to ensure that the

fetus is not impinging on the cord.• Check the fetal heart rate to determine

for fetal distress.

• If the patient claims she can feel a loop of the cord coming out of her vagina (umbilical cord prolapsed), lower the head of the bed (Trendelenberg position) in order to release pressure on the cord.

• Also apply sterile, saline-saturated gauze to prevent drying of the cord, if needed. If labor does not occur spontaneously at the end of 24 hours after membrane rupture, it will be induced ,provided the woman is estimated to be at term.

Signs of True Labor

1. Uterine contractions2. Effacement/Dilatation

In primis, effacement occurs before dilatation (ED)In multis- dilatation proceeds effacement ( DE)

False Vs. True Labor

Parameters for comparison:1. Regularity2. Location3. Changes in contractions4. Absence/presence of contractions during

activity.5. Cervical Changes

False vs. True Labor

FACTOR TRUE LABOR FALSE LABOR

Contractions Produce progressive dilation and effacement of the cervix. Occur regularly and increase in frequency, duration, and intensity.

Do not produce progressive dilatation and effacement. Are irregular and do not increase in frequency, duration, and intensity.

Show Is present. Not present. May have brownish discharge that may be from vaginal exam if within the last 48 hours.

Cervix Becomes effaced and dilates progressively.

Usually uneffaced and closed.

Fetal Movement No significant change, even though fetus continues to move.

May intensify for a short period or it may remain the same.