Characteristics of the obstetric forceps
All obstetric forceps are composed of two separate blades (determined as right and left by reference to their insertion around the fetal head within the maternal vagina), two shanks (shafts) of varying length, and two handles. Forceps are often described as non-rotational or rotational. Nonrotational forceps are ‘held’ together by either an English (non-sliding) lock on the shank or, in the case of rotational forceps, by a sliding lock on the shank. The blades have a cephalic curve to accommodate the form of the baby’s head and are fenestrated (and not solid) to minimize the trauma to the baby’s head during both placement and birth. They also have a pelvic curve to reduce the risks of trauma to the maternal tissues during the birth process.
When the blades are correctly positioned around the fetal skull, the handles will be neatly aligned in the hands of the doctor who applies them and will be noted to ‘lock with ease’. Forceps that do not lock are most commonly incorrectly placed.
Classification of obstetric forceps ( Forceps Delivery)
Forceps operations fall into two categories: mid-and low cavity. Mid-cavity forceps are used when the leading part of the fetal head has reached below the level of the ischial spines; low-cavity forceps are used when the head has descended to the level of the pelvic floor. High-cavity forceps (with the leading part of the fetal head above the level of the ischial spines) are now considered unsafe and a CS will be the preferred method of birth in nearly all cases.
Types of obstetric forceps
These are designed for use in outlet lift-out when the head is on the perineum or to assist the birth of the fetal head at cesarean section. They have a short shank, fenestrated blades with both pelvic and cephalic curves, and an English lock.
Neville–Barnes or Simpson’s forceps
These are generally used for a low- or mid-cavity forceps birth when the sagittal suture is in the anteroposterior diameter of the cavity of the pelvis. Whilst they have cephalic and pelvic curves to the fenestrated blades, the handles are longer and heavier than those of the Wrigley’s. Anderson’s and Haig–Ferguson’s forceps are also similar in shape and size.
These were originally designed to deliver the fetal head at a station at, or above, the pelvic brim. They are now more commonly used for the rotation and extraction of a baby whose head is in the deep transverse or occipuo posterior malpositions. By comparison to the non-rotational forceps, the Kielland’s forceps blades have fenestrated blades with a much-reduced pelvic curve (in order to allow for the safe rotation of the fetus), longer shanks (to enable rotation within the mid-cavity of the pelvis), and sliding lock to allow for correction of any degree of asynclitism of the fetal head. These forceps should be used only by an obstetrician skilled in their application and use, and indeed in many units their use has been abandoned.
Procedure of Forceps Delivery
In addition to the key points outlined for ventouse, i.e. rationale, consent, urinary bladder catheterization, FHR monitoring, and position of the woman’s legs, specific issues to consider are:
• Consideration should be given as to the location of the birth – in the birthing room (lift-out or low-cavity – non-rotational deliveries) or in the obstetric theatre (all other forceps births).
• Unlike the ventouse, inhalational analgesia or a pudendal nerve block with perineal infiltration is unlikely to be sufficient for a forceps birth. In the majority of instances an epidural, if already in situ, maybe topped up, or spinal anesthetics should be administered. These are mandatory before consideration is given to using Kielland’s forceps.
• The forceps should be held discretely in front of the woman (to visualize how they will be inserted per vaginum) and placed around the fetal head. The left blade is inserted before the right blade, with the accoucheur’s hand protecting the vaginal wall from direct trauma.
• The forceps blades come to lie parallel to the axis of the fetal head, and between the fetal head and the pelvic wall. The operator then articulates and locks the blades, checking their application before applying traction. The blades must be repositioned or the procedure abandoned if the application is incorrect.
• Traction should be applied in concert with uterine contractions and maternal expulsive efforts.
• As with the ventouse, the axis of traction changes during the birth and is guided along the curve of Carus, the blades being directed to the vertical as the head crowns.
Complications of instrumental vaginal birth ( Forceps Delivery )
Although forceps are less likely than the ventouse to fail to achieve a vaginal birth, they are significantly more likely to be associated with third- or fourth-degree tears (with or without the concurrent use of an episiotomy), vaginal trauma, use of general anesthesia, flatal, faecal and urinary continence.
Maternal Complications of Forceps Delivery
Complications may include:
• Trauma or soft tissue damage – occurring to the cervix, vagina or perineum.
• Dysuria or urinary retention, which may result from bruising or edema to the tissues around the urethra.
• Perineal discomfort.
• Haemorrhage (both from tissue trauma and also uterine atony – the risk of which is always increased following an assisted vaginal birth).
Neonatal Complications Forceps Delivery
Complications may include:
• Marks on the baby’s face and bruising (commonly caused by the pressure from the forceps blades and around the caput succedaneum/chignon from the ventouse – nearly all of which resolve within 48–72 hours after birth.
• Facial palsy, which may result from pressure from a blade compressing a facial nerve (a transient problem in most instances).
■ Prolonged traction during birth with a ventouse will increase the likelihood of scalp abrasions, cephalohaematoma, or sub-aponeurotic bleeding.
Some authors suggest that failure rates of <1% should be achieved using the correct technique and with well-maintained equipment. Many authors feel that this is an unrealistic target. Failure of the ventouse realistically arises in up to 20% of cases.
The following as factors will often be found to have contributed to failure:
With the ventouse
• Failure to select the correct cup type – inappropriate use of the silastic cup – especially in the presence of deflexion of the fetal head, excess caput, ‘dense’ epidural block or fetal macrosomia (true CPD).
• Failure of the equipment to provide adequate traction as a consequence of a leakage of the vacuum.
• Incorrect cup placement – too anterior or lateral, with or without inclusion of maternal soft tissues within the cup.
With any instrument
• Inadequate initial case assessment – high head, misdiagnosis of the position and attitude of the head.
• Traction along the wrong plane (often too anteriorly and not along the curve of Carus).
• Poor maternal effort with inadequate use of syntocinon to maximize the contribution from coordinated uterine activity.
Whatever the outcome, the midwife in attendance is vital to the success of any maneuvers undertaken, encouraging the mother to be an active participant in her birth, supporting the mother and her partner through what may be perceived to be a ‘deviation from normal’ and importantly, to support the clinician undertaking the assisted birth.