The document discusses the physiology of labor, including theories of labor initiation and signs that labor is impending or has begun. It describes five theories for what triggers the start of labor: the uterine stretch theory; oxytocin theory; progesterone deprivation theory; prostaglandin theory; and aging placenta theory. It also outlines seven common premonitory or warning signs that labor may start soon: lightening; Braxton Hicks contractions; maternal energy; weight loss; cervical changes; rupture of membranes; and bloody show. Finally, it provides diagnostic criteria for differentiating true labor contractions from false labor contractions based on regularity, location, changes over time, and impact of activity, as well as comparing cervical changes.

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

3. 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.

4. 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.

5. Premonitory Signs of Labor
1. Lightening
2. Braxton Hick’s Contractions
3. Sudden burst of maternal energy/activity.
4. Slight decrease in maternal weight
5. Softening “ripening” of the cervix
6. Rupture in the membranes “BOW”
7. Show

6. Premonitory Signs of Labor
1. 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

7. 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

8. 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

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

10. 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.

11. Premonitory Signs of Labor
5. Softening/”ripening” of the cervix
Goodell’s Sign

12. Premonitory Signs of Labor
6. Ruptured BOW
Important nursing considerations:
A. 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.

13. Premonitory Signs of Labor
7. Show
Sudden gush of blood (pinkish vaginal discharge)
Nursing Implication:
Assess for the color of vaginal discharge
* Greenish- meconium stained
* Bright Red- vaginal bleeding

14. Signs of True Labor
1. 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

15. 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.

16. 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.

17. 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.
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.

18. 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.

19. 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.

20. .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.

21. 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.

22. 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.

23. • 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.

24. Signs of True Labor
1. Uterine contractions
2. Effacement/Dilatation
In primis, effacement occurs before
dilatation (ED)
In multis- dilatation proceeds
effacement ( DE)

25. False Vs. True Labor
Parameters for comparison:
1. Regularity
2. Location
3. Changes in contractions
4. Absence/presence of contractions during
activity.
5. Cervical Changes

26. 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.