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Normal Labour

Series of events that take place in the genital organ in an effort to expel the viable product of conception out of uterus through the vagina into the outer world. Labor is defined as the presence of regular uterine contractions with progressive cervical dilation and effacement. OR, The physiological process by which the fetus, placenta and membranes are expelled through the birth canal.

  1. Definition of normal labour
    1. Onset is spontaneous, occurs between 37and 42 weeks gestation.
    2. Culminates in a normal delivery of a live healthy infant.
    3. The process is completed within 24 hours and there are no maternal complications.
    4. With vertex presentation.
  2. Labour is divided into three stages:
    1. First Stage: From the onset of regular painful uterine contractions, accompanied by effacement and dilatation of the os uteri, to full dilatation of the os uteri. (6-18hrs)
    2. Second Stage: From full dilatation of the os uteri to the complete expulsion of the fetus. (30mins –1hour)
    3. Third Stage: From complete expulsion of the fetus to the complete expulsion of the placenta and membranes. (10-20mins)
  3. Causes of Onset of Labour
    1. Uterine distention.
    2. Fetal placental contribution
    3. Alteration of estrogen / progesterone level
    4. Synthesis of prostaglandins
    5. Level of oxytocin.
    6. Neurological factor
  4. Physiology of Labour
    1. During the last trimester of pregnancy, the process of cervical growth and remodeling is accelerated. This process is under the influence of the placental hormones and relaxin. Prostaglandin E2 (PGE2) acts synergistically with these substances to promote cervical change.
    2. At the end of gestation there is increased production of PGE2. Concomitantly, there is an increase in the production and concentration of oxytocin receptors. The number of receptors increases with uterine distention. This also causes an increase in the number of myometrial gap junctions.
    3. As a result of these last two events, there is an increased response by the myometrium to the oxytocin pulses secreted by the posterior pituitary, which then causes an increase in the frequency and intensity of the contractions.
    4. This generates greater pressure and tension on the cervix, which further increases the production of PGE2. This is followed by an increasing frequency of oxytocin pulses that increases the frequency of contractions.
    5. The decidua then responds to the oxytocin by releasing PGF2a, which increases the response to oxytocin by the myometrium. At this point, maturational changes in the placenta and fetus cause the release of a diverse number of substances from several organs. This includes epidermal growth factor, platelet-activating factor, adrenocorticotropic hormone, stress hormones, vasopressin, and increased amounts of oxytocin.
    6. The release of some of these substances is caused by the stress of the transient decrease in fetal oxygenation due to the increased frequency of uterine activity. As a result of the release of these substances, additional mobilization of arachidonic acid from the uterine phospholipids occurs.
    7. This causes an increase in the release of prostaglandins from the placental membranes during the contractions.
    8. This, in turn, is a further stimulus for increased uterine activity. In this way, this process creates a continuous cycle of activity that results in the development of labor.
  5. Identification of labour:

Contraction of true labour

False Labour

Regular intervals

Increase in intensity

Increase in frequenmy

Associated with cervical dilatation

Discomfort in back and abdomen

Not stopped by Sedation

At irregular intervals

Long intervals

Intensity unchanged

No dilatation of cervix

Discomfort in lower abdomen relived by sedation

  1. Features of onset of labour:
    1. Painful uterine contraction.
    2. Show.
    3. Dilatation and effacement of cervix.
    4. Formation of bag of water
  2. Physiology of the first stage of labour
    1. Onset is a process and not an event – cervical ripening from 36 weeks gestation in the primigravida
    2. Contractions – increase in length strength and frequency
    3. Cervix effaces and dilates
    4. Upper segment shortens and thickens - retraction
    5. Formation of forewaters - General fluid pressure
    6. Fetal axis pressure


____________Another Depiction of the formation of the Lower uterine segment__________

  1. Clinical importance of lower segment:
    1. CS is performed through this segment
    2. Implantation of placenta in lower segment gives rise to placenta previa.
    3. Morbid adherent placenta.
    4. PPH- Poor retractile property.
    5. Rupture uterus through this segment.
    6. Enables expulsion of fetus
  2. Physiology of the second stage of labour
    1. Contraction and retraction continue
    2. Descent and rotation of presenting part
    3. Presenting part meets resistance of pelvic floor
    4. Ferguson’s Reflex – contractions become more expulsive in nature
    5. Involuntary pushing by mother accompanies the contractions
    6. Displacement of the pelvic floor
    7. Expulsion of the fetus – The mechanism of labour

  3. Physiology of the third stage of labour
    1. Contraction and retraction – placental site reduced in size by 50%
    2. Placental separation – placenta compressed by contracting uterus and blood in intervillous spaces forced back into veins of decidual layer.
    3. Residual fetal blood escapes down cord to neonate and further compression of placenta takes place.
    4. Pressure in veins of decidual layer now leads to rupture and placenta detatches from uterine wall.
    5. Control of bleeding – oblique uterine muscle fibres contract to ligate torn vessels. Blood loss 60 – 100mls
    6. Expulsion of the placenta – by gravity or maternal effort.
  4. Mechanism of separation of placenta:
    1. Plane of separation runs through the spongy layer of deciduas basalis.
    2. Two ways of separation of placenta.
      1. Central (Schultze).
      2. Marginal (Mathews-Duncan)
​​​Remember: S.S.C = Shiny Schultz Central.
  1. Mechanism of control of bleeding:
    1. Complete retraction
    2. Thrombosis.
    3. Apposition of the walls of uterus
  2. Mechanism of Normal Labour
    1. In 70% of cases head enters the brim through transverse diameter.
    2. Diameter of engagement is available transverse diameter of inlet.
    3. Engaging diameter of head is sub-occipito bregmatic (9.5cm) or sub-occipito frontal (10cm.)

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