Normal labour

1. NORMAL LABOR

2. LABOR
• DEFINITION :- series of events that takes place in the genital organ in an
effort to expel the viable products of conception ( fetus, placenta and the
membrane ) out of the womb through the vagina into the outer world is
called ‘labor’.

3. NORMAL LABOR
(EUTOCIA)
• DEFINITION:- Labor is called normal if it fulfils the following 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 complication affecting the health of the mother and/or
the baby.

4. CAUSES OF ONSET OF LABOR
It is unknown but the following theories were postulated:
1) Hormonal factors
2) Mechenical factors
3) Neurological factors

5. Hormonal factors
oestrogen:-
Increase release of oxytocin from maternal pituitary.
• Promote synthesis of myometrial receptors for oxytocin by 100-200 folds
,prostaglandin synthesis and increase gap junction in myometrial cells.
• Acc. Lysosomal disintegration in the decidual and amnion cells resulting in increased
prostaglandin (PGF2a) synthesis
• Stimulate the synthesis of myometrial contractile protein –actomyosin through
Camp.
• Increase the excitability of the myometrial cell membranes.

6. Hormonal factors
• Progesterone withdrawl theory
• Before labour , there is a drop in progesterone as the cortisol inhibit the conversion
of foetal pregnenolene to progesterone leading to predominance of the excitability
action of oestrogen.
• Prostaglandin theory:
• Prostaglandin E2 and F2a are powerful stimulators of uterine muscle activity by
increasing gap junction . PGF2a was found to be increased in maternal and foetal
blood as well as the amniotic fluid late in pregnancy and during labor which is
triggered by rise in estrogen level , glucocorticoids , mechanical stretching in late
pregnancy, increase in cytokines (IL-6,TNF) infection, vaginal examination.

7. Oxytocin theory
• Although oxytocin is a powerful stimulator of uterine contraction , its natural
role in onset of labor is doubtful. The secretion of oxytocinase enzyme from
the placenta is decreased near term due to placental ischemia leading to
predominance of oxytocin action .
• Large no. of oxytocin receptors present in the fundus than cervix.
• Receptor no. and sensitivity increasing during labor.
• Stimulate prostaglandin (E2 and F2a) synthesis and release

8. Foetal cortisol theory
Cascade of events activate fetal hypothalamic-pituitary-
adrenal axis prior to onset of labor ->increased CRH-> increased release
of ACTH -> fetal adrenals -> increased cortisol secretion -> accelerated
production of estrogen and prostaglandins from placenta.

10. Mechenical factors
• Uterine distension theory
• Like any hollow organ in the body , when the uterus is distended to a certain
limit, it starts to contract to evacuate its contents. This explains the preterm
labor in case of multiple pregnancy and polyhydramnios.
• Stretch of the lower uterine segment:
• By the presenting part near term.

11. Neurological factors
• Both alfa and beta adrenergic receptors are present in myometrium; estrogen
causing the alfa receptors and progesterone the beta receptor to function
predominantly.
• The contractile response is initiated through the alfa receptors of post
ganglionic nerve fibers in and around the cervix, and the lower part of
uterus .

12. Contractile system of myometrium
• The basic elements involved are
• A) actin
• B) myosin
• C) ATP
• D) enzyme myosin light chain kinase (MLCK)
• E) calcium

13. Clinical picture of labor
• Prodormal (prelabor) stage – premonitoring stage- may begin 2-3 weeks before the
onset of true labor in primigravidae and a few days before in multigravidae.
• The features are inconsistent and may consist of the following;-
• Lightening
It is the relief of upper abdominal pressure symptoms as dyspnea , dyspepsia and
palpitation due to :
>descent in the fundal level after engagement of the head and
>shelfing of the uterus.

14. • Cevical changes:- few days prior to onset of labor, cervix become ripe.
• A ripe cervix is soft , admit one finger easily , cervical canal is dilatable.

15. Onset of labour
• It is characterised by :
• True labor pain
• A)
• >it is expelled cervical mucus plug tinged with blood from ruptured small
vessels tinged with blood from ruptured small vessels as a result of
separation of the membranes from the lower uterine segment. Labour is
usually starts several hours to few days after show.

16. • True labor pain False labor pain
1)Regular 1) Irregular
2)Increase progressively in frequency 2) Do not
duration and intensity
3)Pain is felt in abdomen and radiating to 3) pain is mainly felt in the abdomen.
the back.
4)Progressive dilation and effacement of 4)no effect on cervix.
cervix.

17. •True labor pain False labor pain
5)Membrane are bulging during 5) No bulging of the membranes
contraction
6) Not relieved by antispasmodics or 6) Can be relieved by antispasmodic
sedatives. and sedatives.

18. B) SHOW:- expulsion of cervical mucus plug mixed with blood is called ‘show’.
Oozing of blood is due to rupture of capillary vessels of cervix and from the
raw decidual surface caused by separation of membrane due to stretching of
lower uterine segment.
C) Dilation of the cervix:
• > a closed cervix is a reliable sign that labor has not begun . In multigravidae
the cervix may admit the tip of the finger before onset of labor
D) formation of the bag of fore – water :
• >it bulges through the cervix and becomes tense during uterine contraction.

19. Premonitoring
• Blood pressure
• Pulse
• Blood sugar level
• Foetal heart rate
• Contraction - rate
- time
• PV- cervical dilatation
- cervical effacement
- rate of descent of foetus

20. Physiological effects of labor
• On mother
• Temperature : slight >37.5
• Pulse increases upto 100/min
• Blood pressure : systolic blood pressure may rise slightly due to pain , anxiety and stress.
• Oedema and congestion of the conjunctiva .
• Minor injuries : to the birth canal and perineum may occur particularly in primary gravidas
• blood loss from the placental site is 100-200 ml and from laceration or episiotomy is 100ml
so the total average blood loss in normal is 250ml.

21. Physiological effects of labor on foetus
• Moulding:
• The physiological gradual overlapping of the vault bones as the skull is
compressing during its passage in the birth canal .
• One parietal bone overlaps the other and both overlap the occipital and
frontal bones so fontanelles are no more detectable . It is of a good value in
reducing the skull diameters but severe and /or rapid moulding is dangerous
as it may cause intracranial haemorrhage

22. Degree of moulding
• + suture lines closed but not overlap.
• ++ overlap of bone but reducible.
• +++ overlap of the bones but irreducible.

23. • Caput succedaneum:
• A) it is a soft swelling of the most dependent part of the foetal head occurs in
prolonged labor before full cervical dilation and after rupture of the membranes
with poorly defined margins in contrast to cephalhaematoma which is
hemorrhage of blood b/w the skull and periosteum of any age , its boundaries are
limited by individual bones.
• B) it is due to obstruction of the venous return from the lower part of the scalp by
the cervical ring.
• Presence of caput indicates
-Foetus was live during the labor
-Labor was prolonged and difficult
-The attitude of foetal head during labor can be expected as caput is present in the
most dependent part of it.

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