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Assisted Vaginal Delivery – Nonrotational Forceps and Manual Rotation
The Forceps – Historical Context
The invention of the forceps by the Chamberlen family and how the instruments were initially used has been described in Chapter 15 . The addition of the pelvic curve to the design of the forceps ( Fig. 16.1 ) and the subsequent change in the direction of traction during delivery provided the foundation for the technique used in contemporary nonrotational forceps.
André Levret is credited with the introduction of the pelvic curve to forceps, presented to the Paris Academy in 1747, but the principle was also described by Benjamin Pugh, an obstetrician in Essex, in the preface of his 1754 Treatise of Midwifery. Smellie also developed his own design but added the modification of the English lock found on present-day forceps. The pelvic curve enabled the instrument to be used from high in the pelvis, following the curve of Carus (i.e. the pelvic axis) during descent. Nearly half the traction force was dissipated ineffectively against the anterior pelvic wall, and simple bands passed through the fenestration were described by the Danish obstetrician Mathias Saxtorph to counter the problem. A century later, Poullet recommended cords passed through a hole in the blade, below the fenestration, a modification found on Haig–Ferguson forceps. During the mid-19th century, Tarnier added axis-traction to forceps allowing traction to be directed posteriorly during descent of the fetal head. This principle was further refined with instruments including Hubert’s traction bar and detachable traction handles with a wide perineal curve. The latter were attached at the upper or lower part of the handles near the lock (e.g. the Haig–Ferguson and Neville–Barnes forceps, respectively). They are no longer a part of contemporary practice.
Charles Pajot of Paris popularized the manoeuvre of manually pushing down on the shanks while applying outwards traction force. Although still widely known as ‘Pajot’s manoeuvre’, it was first described by Saxtorph and remains an important part of forceps delivery to this day.
Background
The indications for assisted vaginal delivery (AVD) have already been described in Chapter 15 , the most common being prolonged second stage and presumed fetal compromise. Despite being named ‘nonrotational’, they can be safely applied up to 45 degrees away from the maternal sagittal plane (i.e. from right occipitoanterior [ROA] to left occipitoanterior [LOA]). The various parts of the standard forceps are shown in Fig. 16.1 . There are several types of nonrotational forceps in use in modern obstetric practice, which generally only differ in weight and in the length of the shanks/handles. Short-handled forceps (e.g. Wrigley’s) are potentially only useful for outlet forceps delivery from near to the introitus, but are useful for assisting delivery at caesarean section.
When selecting forceps over vacuum, the following should be considered: operator experience, avoidance of sequential instrumentation and, of critical importance, the station and position of the fetal head. The head should be no more than one-fifth palpable abdominally.
A Cochrane systematic review confirmed that forceps are less likely to fail than vacuum, but are associated with an increased risk of maternal trauma. In addition the accoucheur should consider forceps in preference to vacuum for the following indications:
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When maternal effort is compromised
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Face presentation (vacuum contraindicated)
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Delivery <34 weeks (vacuum contraindicated)
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Following multiple attempts at fetal scalp sampling
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Acute fetal compromise
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Mid-cavity delivery.
Preparation and Technique for Nonrotational Forceps
The accoucheur should always consider whether forceps delivery is best undertaken in the delivery room or in the theatre environment (i.e. a ‘trial of forceps’). This will depend on the clinical picture at the time, including the condition of both mother and baby. The majority of forceps deliveries can be undertaken in the delivery room, but the accoucheur must be aware of those cases where there is ‘a significant risk of not achieving vaginal delivery’. Discussion with a senior obstetrician should always occur, with direct supervision of the procedure as needed. The overall incidence of instrumental delivery is 5–20% of all births in high-income countries, with 2–5% occurring in theatre as a ‘trial’. The RCOG recommends that a ‘trial’ should be conducted in theatre where there is immediate recourse to caesarean section. In the presence of fetal compromise, the accoucheur must be mindful that moving to theatre is associated with a statistically significant increase in the mean decision to delivery interval (labour room 14.5 minutes, [standard deviation] SD 9.5 versus operating theatre 30 minutes, SD 14.6). In cases where the fetal head is arrested in the mid pelvis, particularly with the head <2 cm below the ischial spines, there is a higher risk of failure. Factors such as increased maternal body mass index, ‘large for dates’ or estimated weight >4 kg, the head one-fifth palpable per abdomen or malposition of the head also increase the risk of failure. It is prudent to remember that these factors are also associated with an increased risk of shoulder dystocia and postpartum haemorrhage.
The importance of clear communication and careful assessment have been emphasized in Chapter 15 . During assessment, you must carefully relate the findings on abdominal and vaginal examination, ensuring that the true level of the fetal head is clearly defined. Be wary where there is significant caput or moulding. Always remember that a forceps delivery is an opportunity for the accoucheur to assist the woman in her birth and every effort should be made to involve her actively throughout. This should never be a case of the obstetrician ‘taking over’ the delivery. Maintaining rapport with the couple is critical before, during and after the procedure.
‘It is a good working rule never to apply the forceps if the sinciput can still be felt per abdomen. This should be remembered when examining the patient who has been long in labour, for the extreme moulding of the head and the considerable size of the caput succedaneum may give a false impression to the examining vaginal fingers to the degree of descent already achieved.’
J Chassar Moir
Munro Kerr’s Operative Obstetrics. London: Bailliere, Tindal & Cox; 1964.
Key aspects of preparation:
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Team preparation (include neonatal support)
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Confirm consent
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Ensure adequate space for the operator to sit or kneel
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Check swabs, instruments and other essential equipment
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Ensure adequate analgesia (pudendal block, perineal infiltration, regional blockage)
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Position the patient in lithotomy at the edge of the bed – in/out catheterization as appropriate
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Careful clinical assessment before forceps application.
Assembling the Forceps
Ensure that the forceps blades are a matching pair. All forceps have a number imprinted on the handles, shanks or blades and these must match. The forceps are locked together and held in front of the perineum in the same orientation that they will lie within the maternal pelvis. This is known as ‘ghosting’ and is an important step in preparation. Well-applied forceps blades will always lie parallel to the sagittal suture of the fetal head in all positions. However, they should only lie parallel to the maternal sagittal plane in the direct occipito-anterior (DOA) or direct occipito-posterior (DOP) position.
Application of the Blades
Insert the left blade first – the nature of the lock means that this avoids having to ‘uncross’ the handles after application. Fig. 16.2a demonstrates how the left blade is held in the left hand in a vertical position with a ‘light pencil grip’. The index and middle fingers of the right hand are inserted within the introitus at 5 o’clock, facing the fetal skull. Space is made to introduce the tip of the blade. The two fingers are moved laterally to protect the vaginal wall as the blade is fully inserted to lie just in front of the left ear of the fetus. The blade is rotated through 90 degrees along is long axis during the insertion process. The thumb of the right hand helps to guide the blade into position. The blade should never be forced into position but enters ‘under its own weight.’ The forceps handle should be gently pushed downwards against the perineum which will keep it in position during insertion of the right blade.
‘Branche gauche à la main gauche, à gauche la première: tout doit être gauche, sauf l’accoucheur …’
‘Left blade in the left hand, to the left at first; all is gauche, except the skill of the obstetrician …’
Charles Pajot
Travaux d’obstetrique et de gynécologue précédés d’elements de practique obstetricale. Paris: H. Lauwereyns; 1882.
Changing hands, the same procedure is repeated to insert the right blade ( Fig. 16.2b ). Insertion can be more difficult because of the space occupied by the left blade. After insertion the blades will need minor adjustment to close the lock. Avoid holding the handles together as this compresses the head.
Failure of the blades to lock easily, requires the operator to carefully reassess their placement and the position of the fetal head. The blades may need to be removed and reapplied. Use ultrasound to confirm fetal head position and request more senior assistance. The most common reasons for failure to lock are asymmetrical placement of the blades around the fetal head or an unsuspected ROP or LOP position.
Checking Application
Introduce an index finger along the shanks to confirm that the lambdoidal sutures are equidistant from the blades ( Fig. 16.3(A) ), the posterior fontanelle is no more than 1 cm above the plane of the shanks ( Fig. 16.3(B) ), no more than a finger-tip can enter the fenestration from inside the blade ( Fig. 16.3(C) ) and the shanks should be perpendicular to the sagittal suture ( Fig 16.3(D) ) with the blades parallel to the suture.
Correct application means the head is well-flexed with the blades lying along the mentovertical diameter of the fetal skull ( Fig. 16.4 ). With ideal application in the DOA position, the blades will lie symmetrically and parallel to the walls of the pelvis ( Fig. 16.5a ).
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