Normal Labour

Normal Labour

Definition

Labour is the process resulting from uterine contraction leading to expulsion of products of conception from the uterine cavity through vagina.

Normal labour

Labour is called normal when it satisfies the following criteria

·  Spontaneous onset of labour

·  Starts at 38 – 40 weeks

·  Vertex presentation

·  Occipito-anterior position

·  Labour is not unduly prolonged (average 12 hours)

·  No complication to the mother and baby

Causes of onset of labour

·  The exact mechanisms are not known. The theories are,

·  Biological – ageing of conceptus, cell degeneration, hypoxia.

·  Mechanical – myometrial stretch, decidual cell stretch.

·  Hormonal – prostaglandin release, oxytocin stimulation, fetal cortisol production and progesterone withdrawal.

Characteristics of uterine contraction

·  Effective uterine contraction lasts for 30 – 90 secs create 20 – 30 mmHg of intrauterine pressure and occur every 2 – 4 minutes.

·  The pain of contraction is throughout labour to be caused by one or more of the following

·  Hypoxia of the contracted myometrium.

·  Compression of nerve ganglia in the cervix and lower uterus by the tightly interlocking muscle bundles.

·  Stretching of the cervix during dilatation.

·  Stretching of the peritoneum overlying the uterus.

Changes in cervix

Effacement of the cervix: it is the shortening of the cervix. The cervix is pulled up and become a part of the uterine segment. Effacement is expressed as ranging from 0% (no reduction in length) to 100% palpable below the fetal presenting part.

Dilatation of cervix: cervix dilates to a maximum of 10 cm to enable the head to pass through the cervix.

Diagnosis Of Labour

True labour pain:

·  Starts over the back (sacrum) radiates to lower abdomen and thigh.

·  Intermittent colicky pain.

·  Gradually the intensity, duration and frequency of contraction increases.

·  Pain is associated with uterine contraction.

·  Pain is not relieved by enema.

Dilatation of cervix: Progressive dilatation & effacement of cervix

Show: Blood stained mucus discharge per vagina due to separation of the cervical mucus plug.

Stages and Phases Of Labour

First stage: The first stage of labour is the interval between the onset of true pain and full cervical dilatation. Duration is 6-12 hours. The first stage is further divided into a latent and an active phase.

·  Latent phase:

The latent phase extends from the onset of labour till 3 – 4cm dilatation. During this phase, uterine contraction are mild and irregular. They become intense, frequent and regular as the latent phase progress.

·  Active phase:

The active phase is characterized by increased rate of cervical dilatation.

Second stage: The duration of the 2^nd stage averages 2 hours for primi and 30 minutes for multiparaThe 2^nd stage of labour is the interval between full cervical dilatation to delivery of the baby.

Diagnosis of second stage of labour:

·  Bearing down pain with strong uterine contraction.

·  Bulging of the perineum and gapping of the anus.

·  Full dilatation of the cervix.

Third stage: The 3^rd stage of labour is the interval between the delivery of the fetus to delivery of the placenta, umbilical cord and fetal membranes and lasts 15-30 minutes. Separation of the placenta is the result of continuous uterine contraction after delivery of the fetus . The contraction reduces the area of uterine placental bed, with placental separation occurring in the spongiosa layers of the decidua Vera. Blood loss is controlled by compression of spiral arteries by the continued contraction which transport the placenta from fundus into the lower uterine segment and through cervix into the vagina.

Fourth stage: The 4^th stage is the stage of observation for atleast one hour after the expulsion of the placenta and membranes.

Mechanism Of Normal Labour

Definition: A Series of movements adapted by fetus in the birth passage during expulsion.

Mechanism of normal labour falls on: - (3 P’s)

·  Power – strength of contraction

·  Passage – pelvic dimensions and configurations

·  Passenger – size of the baby

Mechanism

a. Engagement:

When the greatest diameter of the presenting part (biparietal diameter in vertex) has passed the plane of the pelvic brim, the head is said to be engaged.It occurs in late pregnancy (primi) or at the time of labour (multi).

b. Descent:

·  The Presenting part descends slowly and progressively.It depends on cephalopelvic relationship

c. Flexion:

·  Good flexion aids engagement and descent.

d. Internal rotation:

·  It occurs on pelvic floor. The resistance of the pelvic floor helps.

·  The head must rotate to anterior (or posterior) to pass ischial spines.

e. Crowning:

·  After internal rotation and further descent, vulva form a crown around the head (i.e.) the biparietal diameter distends the valval outlet without any recession of the head even after contraction is over.

f.  Extension:

·  Distension of perineum by vertex.

·  Occiput beyond symphysis &Head stands out.

g.  Restitution:

·  Untwisting of the neck, head rotates to the position occupied at engagement.

h. External rotation:

·  Shoulder descends in the path similar to that followed by the head and rotates anteroposteriorly.

·  Head swings.

i. Lateral flexion:

·  Anterior shoulder comes under the symphysis pubis.

·  Posterior shoulder sweep the perineum.

j. Expulsion:

After delivery of the shoulder under the symphysis pubis, the rest of the body expelled quickly. Rest of the body expelled with lateral flexion