Physiology of labor

The Physiology of Labor
Prepared by:
Sarah Jane Racal, RN,MAN
Christian University of Thailand

Theories of Labor
Uterine Stretch theory -a hollow organ when stretched to capacity contract and empty.
Oxytocin theory- production of oxtytocin from posterior pituitary gland----contraction of the uterus.
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
Lightening
Braxton Hick’s Contractions
Sudden burst of maternal energy/activity.
Slight decrease in maternal weight
Softening “ripening” of the cervix
Rupture in the membranes “BOW”
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Lightening
This 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 dyspnea
Relief of abdominal tightness

Premonitory signs of labor
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

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

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.

5. Softening/”ripening” of the cervix
Goodell’s Sign

6. Ruptured BOW
Important nursing considerations:
Ruptured BOW
Initial Nursing Action
- Put her immediately in bed and take FHT. Instruct the client not to ambulate---fetal cord compression.
B. Cord Prolapse
Initial 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.

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Sudden 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
Uterine Contractions
The 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 Changes
As 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.
Upper uterine segment– this portion becomes thicker andactive, preparing it to exert the strength necessary to expelthe fetus during the expulsion phase.
Lower uterine segment– this portion becomes thin-walled,supple, and passive so that the fetus can be pushed cut of theuterus easily.
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 Changes
There are 2 changes that occur in the cervix
Effacement
– 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 vernixcaseosa. 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
Uterine contractions
Effacement/Dilatation
In primis, effacement occurs before dilatation (ED)
In multis- dilatation proceeds effacement ( DE)

False Vs. True Labor
Parameters for comparison:
Regularity
Location
Changes in contractions
Absence/presence of contractions during activity.
Cervical Changes

False vs. True Labor

Physiology of labor

by sarahracal

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