Mechanisms of Labour

Question 1

‘normal’ labour

Answer 1

• spontaneous onset
• no artificial interventions
• single cephalic presentation
• vaginal delivery
• 37-42/40
• duration of less than 12 hours primip, 8 hours multip

Question 2

Factors to consider

Answer 2

• powers = sufficient uterine activity including influences e.g epidural/tocolytics
• passenger = fetal size/position/presentation
• passages =uterus, pelvic abnormalities, fetal size/position

Question 3

Descent and Flexion

Answer 3

• effective contractions and retractions exert pressure on fetus resulting in descent
• detal head forced evenly on cervix encouraging further flexion and pressure on membranes
• occiput is now presenting part

Question 4

Optimal positioning for labour

Answer 4

lie - longitudinal
attitude - flexion
presentation - cephalic
position - left/right occipital anterior
engaging diameter - suboccipitobregmatic 9.5cm
denominator - occiput

Question 5

Internal Rotation

Answer 5

• ossiput reaches pelvic floor and rotates anteriorly 1/8th of a circle
• saggital suture now in AP diameter of pelvic outlet
• shoulders remain occipital anterior
• vertex distends perineum, occult travels under pubic arch and begin to crown

Question 6

External Rotation

Answer 6

• head delivered in AP position
• occiput directly anteriorly at delivery
• occiput no longer in line with shoulders
• re aligns once delivered

Question 7

Definitions

Answer 7

lie - long axis of fetus in relation to mother (longitudinal)
attitude - posture of fetus (flexed)
position - relation of denominator to pelvis (breech)
crowning - occurs once head emerges under pubic arch and doesn’t recede without maternal effort
extension - head continues to deliver and now extends over perineum delivering face and chin