mechanism of labour - malposition

Question 1

what is malposition ?

Answer 1

when the fetus is lying longitudinally and is a vertex presentation but is not in the occipito-anterior position, so the occipito-posterior position

Question 2

what are the possible causes and predisposing factors of malposition ?

Answer 2

1. modern lifestyle that consists of less activity and poor posture
2. obesity and raised BMI
3. rotation hindered by android pelvis, arthropod pelvis, anterior placenta, flat sacrum
4. poorly flexed head
5. poor uterine contractions
6. epidural anaesthesia

Question 3

why is the first stage of labour prolonged in cases of malpositio?

Answer 3

1. because unlike occipito-anterior where a rotation of 1/8 of a circle needs to be made , occipito-posterior requires a 3/8th of a circle turn
2. head in the OP position is also often deflexed

Question 4

what are the possible outcomes in the second stage of labour in the case of OP positioning ?

Answer 4

1. long internal rotation of the occiput and delivery as occipito-anterior
2. short internal rotation of the sinciput and delivery as a ‘face to pubes’
3. deep transverse arrest of the head

Question 5

what other rare presentation could be an outcome of the second stage of presentation ?

Answer 5

1. partial extension of the head for a brow presentation

2. full extension of the head to a mento-posterior presentation for a face presentation

Question 6

how does long rotation happen and what is the resulting presentation of the baby ?

Answer 6

1. descent takes place with increasing flexion
2. the occiput becomes the leading part ( touches the pelvic floor first)
3. internal rotation of the head 3/8th of a circle occurs along the right side of the pelvis until it is under the symphysis pubis
   ( resulting presentation :occipito-anterior)

Question 7

how does short rotation happen and what is the resulting presentation ?

Answer 7

1. descent takes place with incomplete flexion
2. the sinciput meets the pelvic floor first
3. occiput rotates backwards by 1/8 of a circle
4. further descent occurs until the root of the nose is hinged just ubder the symphysis pubis
5. flexion occurs releasing the brow, vertex and occiput out of the perineum
   (resulting presentation : face )

Question 8

what is the mechanism of delivery in the face presentation?

Answer 8

extension

Question 9

what happens during failure of OP delivery ?

Answer 9

the occipito-frontal diameter becomes caught just above the ischial spines at the narrow bispinous diameter of the outlet

Question 10

what are the tools or methods used for assisted delivery in a case of OP presentation ?

Answer 10

1. rotation of the head to an occipito-anterior position either manually or with kelland’s forceps
2. vacuum extraction
3. LSCS ( lower segment caesarian section)

Question 11

what are the lengths of each of the diameters of the skull:

1. suboccipito-bregmatic
2. suboccipito-frontal
3. occipito-frontal
4. mento-vertical
5. submento-bregmatic
6. submento-vertical

Answer 11

1. 9.5 cm
2. 10.5 cm
3. 11.5 cm
4. 13.5 cm
5. 9.5 cm
6. 11.5 cm

Question 12

what is the longest length in terms of diameters of the baby’s head ?

Answer 12

mento-vertical at 13.5 cm

Question 13

what are the fetal complications of OP presentation ?

Answer 13

birth trauma
jaundice
admission to the neonatal clinic
low 5 minute apgar score