Obstetric forceps is a double-bladed metal instrument used for extraction of the foetal head.
Long curved obstetric forceps
It consists of 2 blades each of them is 15 inches (37.5 cm) long, crossing each other and lock at the site of crossing. Each is composed of:
- The blade proper (7.5 inches): has 2 curves;
- pelvic curve adapted with the maternal pelvic axis,
- cephalic curve adapted to the foetal head.
- The blade is fenestrated to;
- prevent compression of the head,
- prevent its slippage as the parietal eminences are protruding through the fenestration.
- make its weight lighter.
- The 2 blades are separated by one inch at the tip and 3.5 inches at the centre.
- The shank (2.5 inches):
- It is the part between the blade proper and the handle giving a length for the forceps sufficient to be locked easily outside the vagina.
- Lock: there are 4 types of lock;
- English type: double slot lock.
- French type: screw lock.
- German type: combination of both .
- Sliding lock: present in Kielland’s and Barton's forceps.
- Handle (5 inches): It may be serrated or smooth. A projecting shoulder may be present to facilitate traction.
- Axis traction piece: In mid forceps delivery, a separate piece is attached to the forceps to direct the traction in the direction of pelvic axis i.e. downwards and backwards till the perineum.
- There are 2 common types of axis traction piece:
- Neville- Simpson- Barnes: is the commoner one composed of a single bar attached to the handle just behind the lock.
- Milne-Murray’s: It is composed of 2 bars and a handle to be attached to the blade proper.
- Pajot’s manoeuvre: is an alternative to the use of axis traction piece. Traction on the handle is made by the right hand while the left hand pulls downward on the shank or pushes on the shank from above (Modified Pajot’s manoeuvre).
- There are 2 common types of axis traction piece:
It is a short curved forceps of 11 inches length and used for low and outlet forceps delivery.
It is a long forceps characterised by:
- Minimal pelvic curve which is again nullified by a slight bend between the blade proper and the shank so it is nearly a straight forceps allowing rotation and extraction of the head by a single application.
- A sliding lock: to allow application on asynclitic head.
- Knobs on the handle: on the side of the minimal pelvic curve and should be directed toward the foetal occiput during application.
- Bevelled inner surface of the blades: to minimise foetal head injury.
- Light in weight.
It has a perineal curve to allow application to the after-coming head in breech delivery.
A long forceps characterised by:
- The blade of the posterior branch joins the shank at an obtuse angle corresponding to that between the inlet and outlet pelvic planes.
- A 90 degrees hinge joint between the blade and the shank of the anterior branch.
- A sliding lock.
Indication: transverse arrest especially in a platypelloid pelvis with a flat sacrum.
Action of the Forceps
- Traction: is the main action.
- Rotation: in deep transverse arrest, persistent occipito-posterior and mento-posterior.
Indications of Forceps Delivery
Prolonged 2nd stage
It is prolongation for more than 1 hour in primigravidae or 30 minutes in multiparae. This may be due to:
- Inertia and poor voluntary bearing down.
- Large foetus.
- Rigid perineum.
- Malpositions: persistent occipito-posterior and deep transverse arrest.
- Maternal distress manifested by:
- Pulse >100 beats / min.
- Temperature >38oC .
- Signs of dehydration.
- Maternal diseases as:
- Heart disease.
- Pulmonary T.B.
- Pre-eclampsia and eclampsia.
- Foetal distress.
- Prolapsed pulsating cord.
- Preterm delivery.
- After-coming head in breech delivery.
(During caesarean section
One (used as a lever) or the two blades may be used to extract the head through the uterine incision.
Classification of Forceps Delivery
ACOG (1991) Classification:
|Outlet forceps||The foetal head is at the perineum.
The scalp is visible at the introitus without separating the labia.
Sagital suture is in anteroposterior diameter, right or left occipito-anterior or posterior.
Rotation does not exceed 450.
|Low forceps||The leading point of the skull is at station +2 or more and divided into: i-Rotation ≤450. ii- Rotation >450|
|Mid forceps||The head is engaged, but the leading point is above station +2.|
|High forceps||Not included in the classification. It is abandoned in favour of caesarean section.|
Pre-requisites for Forceps Application
- Anaesthesia: general, epidural, spinal or pudendal block.
- Adequate pelvic outlet.
- Aseptic measures.
- Bladder and Bowel evacuation.
- Contractions of the uterus should be present.
- Dilatation of the cervix should be fully.
- Engaged head.
- Forewater rupture.
- Favourable position and presentation:
- Face presentation.
- After-coming head in breech.
Types of Forceps Application
- Cephalic application: the forceps is applied on the sides of the foetal head in the mento-vertical diameter so injury of the foetal face, eyes and facial nerve is avoided .
- Pelvic application: The forceps is applied along the maternal pelvic wall irrespective to the position of the head. It is easier for application but carries a great risk of foetal injuries.
- Cephalo-pelvic application: It is the ideal application and possible when the occiput is directly anterior or posterior or in direct mento-anterior position.
How to know Right and Left Blades
Putting in consideration that the mother is in the lithotomy position, the blade will be applied with the pelvic curve directed anteriorly and the cephalic curve directed medially. If the blade will be applied to the left maternal side it is a left blade and vice versa.
Technique of Forceps Delivery
In occipito- anterior position
- The left blade is applied first. It is held by its handle between the thumb and fingers of the left hand almost parallel with the right inguinal ligament and passed along the left side of the maternal pelvis between the guiding palm of the right hand and foetal head.
- As the blade passes into the birth canal the handle is carried backwards and towards the midline. It is now the lower blade.
- The fingers of the left hand are introduced along the right side of the pelvis and the right blade is held and passed in the same manner. It is now the upper blade.
- The 2 blades should be locked easily, if not this means that they were not correctly applied and should be removed and re-assess the position of the head.
Clinical checks for correct forceps application:
- The sagittal suture lies in the midline of the shanks.
- The operator cannot place more than a finger tip between the fenestration of the blade and the foetal head.
- The posterior fontanelle is not more than one finger- breadth above the plane of the shanks.
Traction should be:
- gentle by the force of the arm only,
- intermittent with uterine contractions only,
- in correct direction i.e. downwards and backwards till the occiput appears at the vulva, then downwards and forwards.
- The 2 blades are unlocked between contractions to minimise the period of head compression.
Kielland forceps in deep transverse arrest
- The forceps is locked outside with the knobs towards the occiput to know the anterior blade.
- The anterior blade is applied first by one of the following methods:
- The wandering method: The anterior blade is guided into the lateral side of the pelvis with the cephalic curve facing the foetal head. It is then slid over the forehead to fit against the anterior parietal eminence.
- The direct method: when the head is low down in the pelvis, the anterior blade is slid between the head and symphysis pubis with the cephalic curve facing the foetal head.
- The old (classical) method: The anterior blade is applied with the cephalic curve towards the symphysis pubis then it is rotated 1800 to fit with the head. This method is not recommended as the lower uterine segment and bladder may be injured.
- The posterior blade is applied along the concavity of the sacrum.
- The 2 blades are locked, head is rotated and extracted as occipito-anterior.
Complications of Forceps Delivery
- Complications of anaesthesia.
- Extension of the episiotomy.
- Perineal tear.
- Vaginal tears.
- Cervical lacerations.
- Bladder injury.
- Ureteric injury.
- Rupture uterus.
- Bone injuries: to pelvic joints, coccyx or symphysis pubis.
- Pelvic nerve injuries.
- Postpartum haemorrhage: due to lacerations or atony.
- Puerperal infections.
- Remote effects: genital prolapse, stress incontinence, cervical incompetence and genito-urinary fistulas.
- Fracture of the skull.
- Intracranial haemorrhage.
- Facial nerve palsy.
- Trauma to the face, eyes or scalp.
- Asphyxia due to:
- intracranial haemorrhage or,
- cord compression between the head and the forceps.
Failure to extract the foetus by the forceps which may be due to failure to apply the forceps or to deliver the head with it.
- Cephalo-pelvic disproportion.
- Contracted outlet.
- Incomplete cervical dilatation.
- Constriction ring.
- Head is not engaged.
- Malpositions as persistent occipito-posterior.
- Malpresentations as brow.
- Foetal congenital anomalies as hydrocephalus, ascitis and conjoined twins.
- Reassessment: The forceps is removed and the patient is re-examined to detect the cause and correct it if possible.
- Caesarean section: is indicated in uncorrectable causes as cephalo-pelvic disproportion, and contracted outlet.
- Exploration of the birth canal: for any injuries.