Chapter 14 – Instrumental Vaginal Delivery




Abstract




Caesarean section rates are on the rise and this may be partly due to lack of appropriate training and experience in instrumental deliveries as well as medico-legal issues. Since caesarean section performed in the second stage of labour is associated with increased maternal morbidity, an appropriately performed instrumental vaginal delivery may help avoid the unnecessary risks.


Instrumental vaginal deliveries can be hazardous in inexperienced hands and should be undertaken with due care and supervision. Various intrapartum measures may help reduce the need for assisted vaginal delivery such as use of partogram, upright or lateral maternal position, one-to-one support to the woman in labour, delayed pushing in women having epidural anaesthesia or judicious use of oxytocin in the second stage of labour, especially in women with epidural anaesthesia.





Chapter 14 Instrumental Vaginal Delivery


Vikram Sinai Talaulikar and Sabaratnam Arulkumaran




Key Facts


Definition Use of obstetric forceps or ventouse (vacuum) to expedite vaginal delivery of a fetus.


Types Either of the two instruments, forceps or ventouse, may be chosen for the delivery. The procedures are classified as (1) mid-cavity, (2) low and (3) outlet (Table 14.1) [1].


Incidence Between 5% and 15% of all vaginal deliveries are assisted by an instrument. Incidence varies depending on population, institution and individuals performing the procedure. In modern obstetrics, use of ventouse has gained popularity, as it can be performed with less profound anaesthesia and is associated with lower risk of maternal trauma.




Table 14.1 Classification for instrumental vaginal delivery



















Outlet


  • Fetal scalp visible without separating the labia. Fetal skull has reached the pelvic floor. Sagittal suture is in the anteroposterior diameter or right or left occiput anterior or posterior position (rotation does not exceed 45°)



  • Fetal head is at or on the perineum

Low


  • Leading point of the skull (not caput succedaneum) is at station plus 2 cm or more and not on the pelvic floor rotation of 45° or less from the two subdivisions:



  • Occipito-anterior position rotation of more than 45° including the occipito-posterior position

Mid


  • Fetal head is no more than one-fifth palpable per abdomen



  • Leading point of the skull is above station plus 2 cm but not above the ischial spines



  • Rotation of more than 45° from the two subdivisions:



  • the occipito-anterior position including the occipito-posterior position

High Not included in the classification, as operative vaginal delivery is not recommended in this situation where the head is two-fifths or more palpable abdominally and the presenting part is above the level of the ischial spines


Adapted from the American College of Obstetrics and Gynecology, 2000 [1].


Key Implications


Caesarean section rates are on the rise and this may be partly due to lack of appropriate training and experience in instrumental deliveries as well as medico-legal issues. Since caesarean section performed in the second stage of labour is associated with increased maternal morbidity, an appropriately performed instrumental vaginal delivery may help avoid the unnecessary risks.


Instrumental vaginal deliveries can be hazardous in inexperienced hands and should be undertaken with due care and supervision. Various intrapartum measures may help reduce the need for assisted vaginal delivery such as use of partogram, upright or lateral maternal position, one-to-one support to the woman in labour, delayed pushing in women having epidural anaesthesia or judicious use of oxytocin in the second stage of labour, especially in women with epidural anaesthesia.


About 27% of fetal head positions diagnosed clinically on digital vaginal examination were found to be incorrect when checked with ultrasonography [2]. This demonstrates the importance of continued training, supervision and review of practice in the area of instrumental deliveries.


On the medico-legal side, clinical negligence claims may arise due to delay in delivery, inappropriate choice of instrument or excessive use of force during delivery and maternal/fetal trauma. In cases of fetal distress it is essential that the instrumental delivery be straightforward, as the combination of trauma and hypoxia is potentially damaging to the fetus. Careful documentation of events immediately after delivery is of paramount importance.



Key Pointers


Indications for assisted vaginal delivery are the following.


Maternal




  • Exhaustion with non-progressive pushing efforts



  • Medical conditions such as severe cardiac, respiratory, cerebrovascular disease or severe hypertension and where pushing is not possible, for example, paraplegia/tetraplegia or myasthenia gravis



  • Proliferative retinopathy


Fetal




  • Fetal compromise manifest by pathological cardiotocograph (CTG) findings or cord prolapse in second stage of labour



  • To control after-coming head of breech


Combined




  • Prolonged non-progressive second stage of labour with risk of damage to maternal pelvic floor and risk of trauma and hypoxia to the fetus. Prolonged second stage may be defined as [3]




    • Nullipara: 2 hours without regional anaesthesia and 3 hours with regional anaesthesia



    • Multipara: 1 hour without regional anaesthesia and 2 hours with regional anaesthesia



However, it is important to recognise that no rigid time limits should be set and the decision to intervene should take into consideration various maternal and fetal factors in labour.



Key Diagnostic Signs


Before forceps or ventouse are applied, the following prerequisites should be fulfilled.


These may be summarised as ‘F O R C E P S’ [4]:


F – Fully dilated cervix


O – Obstruction ruled out (by abdominal and vaginal examination)


Abdominal examination: No more than one-fifth of the fetal head should be palpable on abdominal examination. This ensures that the head has descended to at least beyond the ischial spines to +1 station or lower.


Vaginal examination: Station of the fetal head should be identified in centimetres above or below the ischial spines (Figure 14.1). Ideally the station should be below spines, with descent of the head with contraction and bearing-down effort.





Figure 14.1 Fetal head in relation to the maternal pelvis; 0 station refers to the level of ischial spines. An engaged fetal head will be two-fifths or less palpable on abdominal examination.


Placement of sutures and fontanelles should be identified. The inverted Y-shaped suture lines or overlapping of parietal bones over the occipital bones in labour help to identify the posterior fontanelle. The anterior fontanelle is felt as a soft diamond-shaped depression at junction of four bones. If the anterior fontanelle is felt easily near the centre of the pelvis it indicates the possibility of a deflexed head.


If the amount of caput succedaneum makes examination difficult, then feel anteriorly for the fetal ear. Care should be taken to feel the pinna and the canal, as the ear can be folded and give a false impression of its position. Also, since the ear is just below the biparietal diameter, it can aid in judging the descent of the head.


Synclitism is assessed by feeling the relationship of the sagittal suture to the transverse plane of the pelvic cavity. Anterior asynclitism, in which the anterior parietal bone is more easily felt and the sagittal suture is further back in the transverse plane, is normal. Posterior asynclitism, however, may be a sign of disproportion [5].


Excessive caput succedaneum (soft tissue swelling of fetal scalp) and ‘moulding’ (over-riding of fetal skull bones) may suggest the possibility of cephalopelvic disproportion (Figure 14.2).





Figure 14.2 Caput succedaneum and moulding. (a) Normal fetal scalp with suture separating the skull bones. (b) Caput succedaneum. (c) Grade 1 moulding with apposition of skull bones. (d) Grade 2 moulding with overlap of skull bones reducible with gentle pressure. (e) Grade 3 moulding with overlap of skull bones irreducible with gentle pressure.


Clinical assessment of the bony pelvis has limitations but with experience, obstetricians may be able to judge how well a given fetal head fits the pelvis in particular circumstances to arrive at the decision for a safe instrumental delivery.




  • R – Membranes should have Ruptured and instrument checked and assembled correctly.



  • CCatheterise or ensure that the bladder is empty. Consent the patient appropriately.





  • EExplain the procedure, check the need for Epidural anaesthesia or other pain relief and whether Episiotomy will be needed.



  • P – Confirm Position of head and adequate Power (uterine contractions).



  • S – Determine Station of the fetal skull in relation to ischial spines.



Once it is confirmed that all the aforementioned criteria have been met, follow appropriate steps of delivery and repair any perineal tears or episiotomy.


Go back to check the baby’s head to confirm the positioning of the instrument used and document the details of delivery completely including indication, discussion, consent, precise description of station, moulding, caput succedaneum, position and degree of flexion of fetal head. Description of the procedure should include manoeuvres, rotation, traction, degree of difficulty and number of pulls. The amount of estimated blood loss should be noted. Associated episiotomy or vaginal lacerations and repair should be described in detail.



Key Actions


Introduce yourself to the woman and her partner and explain the reason for instrumental vaginal delivery. It is important to document the discussion with the woman as regards options of waiting, assisted delivery or caesarean section.


Carry out thorough abdominal and vaginal assessment and explain the findings and plan of action to the woman. Verbal or written consent must be obtained as appropriate.


Provide adequate analgesia in the form of epidural or spinal anaesthesia, pudendal block or local anaesthetic infiltration (20 mL of 1% lignocaine) of perineum. The amount of anaesthesia required will depend on level of fetal head and need for rotation. Usually ventouse deliveries require less analgesia. In cases of cord prolapse, antepartum bleeding or prolonged deceleration actions should proceed with a brisk speed.


Oxytocin infusion may be considered if uterine contractions are inadequate (fewer than four in 10 minutes and lasting less than 40 seconds each) in the absence of signs of fetal compromise.




  • The vulva and perineum should be cleansed. The bladder should be empty.



  • Lithotomy position (with slight lateral tilt) is the preferred maternal position.



  • Inform the neonatologist at the start of the procedure.


The choice of instrument will depend on the operator’s experience, station of fetal head and position of the vertex. Ventouse should not be used to deliver babies below 34 weeks and those with suspected bleeding tendencies. In general, ventouse is preferred when the position is occipito- transverse (OT) or occipito-posterior (OP) to allow for autorotation of the fetal head during traction unless the accoucher is experienced in Kielland’s rotational forceps delivery. Where maternal expulsive efforts may be compromised, forceps may be better than ventouse delivery. The failure rates are higher with ventouse as compared with forceps. In most cases the ventouse cup detaches in the lower pelvis almost at the introitus and the delivery is completed via an outlet forceps. Hence the contradiction that with ventouse there are more failed cases but the caesarean deliveries are fewer. If the cup slips higher up use of forceps is not advisable.

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May 9, 2021 | Posted by in OBSTETRICS | Comments Off on Chapter 14 – Instrumental Vaginal Delivery
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