The document defines labor as the process by which the fetus is expelled from the uterus through the vagina. Labor is considered normal when a full-term fetus in the vertex position is delivered within 24 hours through natural efforts alone. Key factors that contribute to the initiation of labor include uterine distension from fetal and amniotic fluid growth, fetal and placental hormones like estrogen and prostaglandins, uterine contractions stimulated by oxytocin, and neurological signals. The mechanism of uterine contractions involves calcium, myosin, actin, and other proteins. Retraction of the uterine muscles is also an important component of labor.

2.  Definition
Series of events that take place in the genital
organs in an effort to expel the viable products of
conception out of the womb through the vagina
into the outer world is called labour

3.  Labour is normal when a full_term fetus
presenting by the vertex is expelled by natural
efforts, within a period of 24 hours.
 It should fulfil the folloing criteria;
1.Spontaneous in onset and at term
2.With vertex presentation .
3.Without undue prolongation.
4.Natural termination with minimal aids.
5.Without having any complications affecting
the health of the mother and/or the baby.

6. (1) Uterine distension;
Stretching effect on the myometrium by the growing fetus and
liquor amnii.
Uterine stretch increases :
 gap junction protiens.
 receptors for oxytocin.
 specific contraction associated protions-(CAPS).
(2) Fetoplacental contribution;
Cascade of events activate fetal HPA axis prior to onset
of labour→increased CRH→increased release of ACTH→fetal
adrenals→increased cortisol secretion →acclerated production
of oestrogen and prostaglandins from the placenta.

7. 3. Oestrogen;
 increases the release of oxytocin from maternal
pitutary.
 promotes the synthesis of myometrial receptors for
oxytocin, prostaglandins and increase in gap
junctions.
 accelerates lysosomal disintegration in the
decidual and amnion cells resulting in increased
PGF2 synthesis.
 stimulates the synthesis of myometrial contractile
protein,
 increases the exitability of the myometrial cell
membranes

8. 4.Progesterone:
-Increased fetal production of DHEA-S and
cortisol inhibits the conversion of fetal pregnenolone
to progesterone.Progesterone levels therefore fall
before labour.
5. Prostaglandins:
 These initiates and maintains the labour.
 Sites of synthesis-amnion,chorion,decidual
cells,myometrium.
 Synthesis is triggered by_rise in oestrogen
level,glucocorticosteroids,mechanical stretching
in late pregnancy,increase in
cytokines,infection,vaginal examination.they also
enhance gap junction formation.

9. 5. Oxytocin and myometrial oxytocin receptors;
(a) Large number of oxytocin receptors are present
in fundus compared to lower segment of cervix.
(b) Receptor number increases maximum during
labour.
(c) Receptor sensitivity increases .
(d) Oxytocin stimulate synthesis and release of PGs.
6. Neurologic factor:
-Although labour may start in denervated
uterus ,it may also be initiated through nerve
pathways.oestrogen causing the α receptors and
progesterone the β receptors to function
predominantly.

10. It consists of
 Actin
 Myosin
 ATP
 Myosin light chain kinase
 Calcium

11. Intracellular calcium
↓
Calmodulin calcium
↓
MLCK
↓
phosphorylated
myosin+actin
↓
Myometrial contraction
Decrease of intracellular
calcium.
↓
Dephosphorylation of
myosin light chain
↓
Inactivation of MLCK
↓
Myometrial relaxation.

12.  Found more in primi.
 Appears prior to onset of true labour pain.
 Probably due to stretching of the cervix and
lower uterine segment due to irritation of
ganglia.

13. This may begin 2 to 3 weeks before the onset of
true labour in primi and a few days before in
multiparae.
The features are;
1. LIGHTENING.
Few weeks prior to onset of labour ,the
presenting part sinks into true pelvis,due to active
pulling up of the lower pole of uterus around the
presenting part.This diminishes the fundal height and
minimises the pressure on diaphragm.Thereby
mother experiences relief.As it rules out
CEPHALOPELVIC DISPROPORTION ,it is a
“WELCOME SIGN”

15. 2.CERVICAL CHANGES:
Cervix become RIPE few days prior to
labour.RIPE cervix is less than 1.5cm in
length,admits a finger easily and is dilatable.

16. - it is characterised by
 Uterine contractions at regular intervals
 Frequency of contractions increased gradually
 Intensity and duration of contractions increased
progressively
 Associated with SHOW
 Formation of bag of forewaters
 Progressive effacement and dilation of the cervix
 Decent of the presenting part
 Not relieved by enema or sedative

17. False labour pains are
 Dull in nature
 Confined to lower abdomen and groin
 Not associated with hardening of the uterus
 They have no other features of true labour pains
 Relieved by enema and sedative
Labour pain
 Throughout pregnancy, painless BRAXTON HICKS
contractions with simultaneous hardening of the
uterus occur.
 These contractions change their character, become
more powerful, intermittent associated with pain
and felt in front of the abdomen or radiating towerds
the thighs

18.  Show
 Expulsion of cervical mucus plug mixed with blood is
called show
 With onset of labour, there is profuse cervical
secretion .simultaneously, there is slight oozing of
blood from the rupture of capillary vessels of the
cervix and from the raw decidual surface.
 Dilation of internal os
 With the onset of labour pain, the cervical canal
begins to dilate more in the upper part than in the
lower, the former being accompanied by
corresponding stretching of the lower uterine
segments.

19.  Formation of bag of water
 Due to stretching of the lower uterine segment,the
membranes are detached easily because of its loose
attachment to poorly formed decidua.
 With the dilatation of the cervical canal , the lower
pole of the fetal membrane become unsupported and
tends to bulge into the cervical canal.
 As it contains liquor which has passed below the
presenting part,it is called “bag of water”

20.  During pregnancy there is marked
hypertrophy and hyperplasia of the uterine
muscle.
 At term the length of the uterus measures
about 35cm.
UTERINE CONTRACTION IN LABOUR:
 Throughout pregnancy there is irregular
involuntary spasmodic uterine contractions
and are painless{BRAXTON HICKS}and have
no effect on cervix dilatation.

21.  Pacemaker of uterine contraction _is situated in the
TUBAL OSTIA from where waves of contractions
spread downwards.
 Good synchronisation of the contraction waves from
both halves of the uterus.
 there is fundal dominance with gradual diminishing
contraction wave through midzone.
 waves of contraction follow a regular pattern.
 intra_amniotic pressure rises beyond 20mm hg during
uterine contraction .
 good relaxation occurs in between contraction to bring
down intra_amniotic pressure to less than 8mm
hg.contraction of fundus lasts longer than that of
midzone.

22.  During contration , uterus becomes hard &
pushed anteriorly to make long axis of uterus
in line with that of pelvis.
PROBABLE CAUSES OF PAIN:
 myometrial hypoxia during contraction.
 stretching of peritonium over the fundus.
 stretching of the cervix during dilation.
 compression of nerve ganglion.
 Pain of uterine contraction distributed along
T10 toL1 , whereas pain of cervical dilatation
is refered to back through the sacral plexus.

23. Tonus:
 The intrauterine presssure in between
contractions.tonus during pregnancy_2-3mm
hg & tonus during labour is 8-10mm hg.
 Factors which govern tonus-
 contractility of uterine muscles.
 intraabdominal pressure.
 overdistension of uterus as in twins &
hydromnios.

24. INTENSITY:
 It discribes the uterine systole.
 Intensity gradually increases with advancement of
labour & becomes maximum during second stage.
 Intrauterine pressure-
 First stage-40 to 50 mm hg.
 second stage-100 to 120 mm hg.
 third stage-inspite of diminished pain the pressure
remains same as second stage, due to lack of
stretching effect.

25. DURATION:
 In the first stage ,contraction lasts for 30 secs
but gradually increase in duration with
progress of labour.
FREQUENCY:
 In early stage , the contractions come at
intervals of 10 to15 minutes.but the interval
gradually shorten with advancement of labour
i.e,every 2-3 minutes.

26. RETRACTION:
 Retraction is a phenomenon of the uterus in
labour in which the muscle fibres are
permanently shortened.
 Unlike other muscles of the body,the uterine
muscles have this property to become
SHORTENED ONCE FOR ALL.
CONTRACTION is temporary reduction in
length of fibres, which attain their full length
during relaxation.In contrast, RETRACTION
results in permanent shortening once & for all.

27. EFFECTS OF RETRACTION IN NORMAL
LABOUR:
 Essential property in the formation of lower
uterine segment & dilatation &effacement of
cervix.
 to maintain the advancement of presenting part
& to help in ultimate expulsion of the fetus.
 to reduce the surface area of the uterus
favouring separation of placenta.
 effective haemostasis after the separation of
placenta.