Mechanism of labour

Question 1

What are the theories of the causes of labour initiation?

Answer 1

1- functional loss of pregnancy maintenance factors
2- synthesis of factors that induce parturition
3- mature fetus (initial signal for parturition start)

Question 2

What are the functions of the decidua?

Answer 2

1- suppress immunity from gestation
2- at end of pregnancy -> eliminates immunity suppression & induces inflammatory signals

Question 3

What are the functions of the cervix during pregnancy?

Answer 3

1- maintains the epithelial barrier to protect reproductive tract from infection
2- sustaining cervical competence despite greater gravitational forces as the fetus grows
3- Extracellular matrix changes that allow progressively greater tissue compliance

Question 4

What are the functions of the placenta?

Answer 4

1- produces sex steroid hormone, growth factors & other mediators that aid transition to parturition
2- barrier or shield to protect from parturition
3- protective tissue layer & immunological acceptance (enzymes)

Question 5

What are the phases of labour?

Answer 5

Phase 1: Quiescence (prelude to parturition)
- cervical softening
- contractile unresponsiveness

Phase 2: Activation (Preparation for labour)
- cervical ripening
- uterine preparedness

Phase 3: Stimulation (process of labour)
- cervical dilatation
- uterine contraction
- fetal & placenta expulsion (the 3 stages of labour)

Phase 4: Involution (parturition recovery)
- cervical repair
- uterine involution
- breast feeding

Question 6

What is the denominator for every presentation?

Answer 6

• vertex (flexed) -> occiput
• brow (deflexed) -> frontal
• face (extended) -> mentum
• breech -> sacrum
• shoulder -> acromion/scapula

Question 7

What is the normal mechanism of labour?

Answer 7

1- engagement
2- descent
3- flexion & internal rotation
4- extension
5- external rotation
6- expulsion

Question 8

What occurs during engagement?

Answer 8

• passage of biparietal diameter through pelvic inlet
• occurs in weeks of pregnancy or at onset of labour (primigravidas)
• if head is not engaged -> floating head

Question 9

How does descent occur?

Answer 9

May not occur till second stage of labour, in multipara with engagement
1- direct myometrial pressure of the fundus upon breach with contractions
2- bearing-down efforts of maternal abdominal muscles
3- extension & straightening of the fetal body

Question 10

When does flexion occur?

Answer 10

When fetal head comes into contact with the pelvic floor -> cervical flexion -> sub-occipito bregmatic will be the presenting part

Question 11

What is the importance of Sub-occipito bregmatic diameter?

Answer 11

The fetal skull has a smaller diameter -> assists in the passage through the pelvis

Question 12

Why is the internal rotation essential during labour?

Answer 12

Changes the occiput from transverse to anterior position -> essential for completion of labour

Question 13

What is the importance of extension during labour?

Answer 13

Allows the occiput to slip beneath the suprapubic arch as the head extends & the nape of the neck is pivoting against the arch

Question 14

When is episiotomy needed?

Answer 14

During crowning

Question 15

What is the importance of restitution & external rotation?

Answer 15

• Restitution -> head aligns itself with shoulders
• External rotation -> brings shoulders AP to be delivered

Question 16

How does expulsion occur?

Answer 16

The anterior shoulder appears under the symphysis pubis -> the perineum becomes distended by the posterior shoulder -> after delivery of the shoulders the rest of body

Question 17

What is molding?

Answer 17

Changes in body fetal head shape as a result not external compressive forces