A forceps is an instrument designed to aid in the delivery of the fetus by applying traction to the fetal head. Many different types of forceps have been described and developed throughout time. Generally, forceps consist of 2 crossing shafts that are maneuvered into a proper relationship with the fetal head and are articulated.

Forceps have 4 major components, as follows:

1. Blades: Each blade has 2 curves. The blades are oval or elliptical and can be fenestrated or solid. They have a concave surface and a convex surface, which are applied to the fetal head and the pelvic curvature, respectively.

2.      Shanks: These connect the blades to the handles and provide the length of the device. They are either parallel or crossing.

3.      Lock: Many different types have been designed. The lock is the type of articulation between the shanks.

4.      Handles: These are the location where the operator holds the device and applies traction to the fetal head.

History of the Procedure: The history of obstetrical forceps is long and, often, colorful. Sanskrit writings from approximately 1500 BC contain evidence of single and paired instruments; Egyptian, Greek, Roman, and Persian writings and pictures refer to forceps.

The credit for the invention of the precursor of the modern instruments used on live infants goes to Peter Chamberlain (circa 1600) of England. Modifications have led to more than 700 different types and shapes of forceps. In 1745, William Smellie described the accurate application to the occiput, rather than the previously performed pelvic application, regardless of the position of the head. In 1845, Sir James Simpson designed a forceps that was calculated to appropriately fit both cephalic and pelvic curvatures. In 1920, Joseph DeLee further modified that instrument and presented the concept of prophylactic forceps delivery.

Clinical studies performed before the 1970s suggested that the risk of fetal morbidity and mortality was higher when the second stage of labor exceeded 2 hours .However, using current obstetrical management, morbidity rates no longer increase with longer labors if fetal surveillance is reassuring. Thus, the length of the second stage of labor no longer is an absolute indication for operative termination of labor.

Other factors were at work to decrease the use of forceps deliveries. In particular, the availability of blood products and greater choices in antibiotics helped make cesarean delivery a safe alternative to operative vaginal deliveries.

Frequency: The frequency of operative vaginal deliveries is estimated to be approximately 10% of all vaginal deliveries.

Simpson forceps was the type most commonly used for outlet and low forceps deliveries. Other types of forceps also are available. Their use is even more controversial. Of these, the most common is the Piper forceps, which is used in the delivery of the after-coming head in breech vaginal deliveries. It is designed to decrease traction on the fetal neck during breech delivery. Multiple other types of forceps have been designed to rotate the fetal head or for unusual maternal pelvic shapes. For detailed information on these more unusual forceps procedures, the reader is directed to the excellent book by Dennen, Dennen's Forceps Deliveries.

Clinical: Forceps delivery is classified according to the level and position of the head in the birth canal at the time the forceps are applied. In 1965, the American College of Obstetricians and Gynecologists issued their classification of low and outlet, mid, and high forceps. Each of these could be interpreted differently according to the operator's understanding of the issue. The low and outlet forceps categories were very restrictive and were applied when the fetal scalp was visible, when it had reached the pelvic floor, and when the sagittal suture was in an anteroposterior diameter of the pelvis. The bigger issue was the broad category of mid forceps applications. It included many stations of the fetal head, from engagement at zero station all the way to the perineum.

For these reasons, the American College of Obstetricians and Gynecologists (American College of Obstetricians and Gynecologists, 2000) redefined the classification of station and types of forceps deliveries in 1988. The revised classification uses the level of the leading bony point of the fetal head, in centimeters, measured from the level of the maternal ischial spines, to define station (-5 to 5 cm).

Criteria for types of forceps deliveries

Outlet forceps: (1) The scalp is visible at the introitus, without separating the labia. The fetal skull has reached the pelvic floor. (2) The sagittal suture is in anteroposterior diameter, right or left occiput anterior or posterior position. (3) The fetal head is at or on the perineum. (4) Rotation does not exceed 45°.

Low forceps: The leading point of the fetal skull is at a station greater than or equal to +2 cm and is not on the pelvic floor; any degree of rotation may be present.

Mid forceps: The station is above +2 cm, but the head is engaged.

High forceps: This is not included in the classification.

Obstetric pelvic evaluation and its clinical implications

The important points of interest are emphasized as follows:

For obstetric purposes, the coccygeal mobility and the narrowness of the subpubic arch should be evaluated during the pelvic examination.

The distance between the symphysis pubis and the sacral promontory is measured by digital examination and is defined as the diagonal conjugate.

The obstetrical conjugate, estimated by subtracting 1.5-2 cm from the diagonal conjugate, is important in determining the capability of the presenting part to pass through the pelvic inlet. Unfortunately, no clinical means of direct midpelvic measurement is available. These measurements can only be obtained with detailed imaging studies.

Furthermore, assessing the pelvic outlet is important. The distance between the ischial tuberosities should be at least 8 cm.

During the examination, one may have a high index of suspicion of a contracted mid pelvis if the ischial spines feel quite prominent, the sidewalls are convergent, and the concavity of the sacrum is very shallow. If the biischial diameter of the pelvis is less than 8 cm, a contracted pelvis should be suspected.

For the purpose of assessing a patient for forceps application, the best time to evaluate the pelvis is at the time of delivery, not at the first prenatal visit.

Indications for operative vaginal deliveries are identical for forceps and vacuum extractors. No indication for operative vaginal delivery is absolute.

The following indications apply when no contraindications exist:

• Prolonged second stage: (1) This includes nulliparous woman with failure to descend for 2 hours without, and 3 hours with, conduction anesthesia. (2) It also includes multiparous woman with failure to descend for 1 hour without, and 2 hours with, conduction anesthesia.

·         Suspicion of immediate or potential fetal compromise is an indication.

·         Shortening of the second stage for maternal benefits: Maternal indications include, but are not limited to, exhaustion, bleeding, cardiac or pulmonary disease, and history of spontaneous pneumothorax.

·         In expert hands, fetal malpositions, including the after-coming head in breech vaginal delivery, can be indications for forceps delivery.

Prerequisites for forceps delivery include the following:

• The head must be engaged.

·         The cervix must be fully dilated and retracted.

·         The position of the head must be known.

·         The type of pelvis should be known.

·         The membranes must be ruptured.

·         No disproportion should be suspected between the size of the head and the size of the pelvic inlet and mid pelvis.

·         The patient must have adequate anesthesia.

·         Adequate facilities and supportive elements should be available.

·         The operator should be fully competent in the use of the instruments and the recognition and management of potential complications.

·         An operator should be present who knows when to stop, to not force the issue, and to not aggressively use both forceps and vacuum in combination because this has been shown to increase morbidity for both the mother and fetus.

Relevant Anatomy:

Planes and diameters of the pelvis

For obstetrical purposes, the pelvis is described as having 3 imaginary planes, as follows 

Plane of the inlet: Four diameters have been described.

• Anteroposterior diameter: This is the distance between the sacral promontory and the symphysis pubis; it is designated the obstetrical conjugate. This conjugate normally measures approximately 10 cm or more, but it may be shortened considerably in an abnormal pelvis.

·         Transverse diameter: This is the greatest distance between the linea terminalis on either side of the pelvis. This imaginary line usually intersects the obstetrical conjugate at a point approximately 4 cm in front of the promontory.

·         Two oblique diameters: Each of these diameters extends from one of the sacroiliac joints to the iliopectineal eminence on the opposite side of the pelvis. These diameters normally average less than 13 cm each.

Plane of the mid pelvis: This is the plane of the smallest dimensions. This plane is extremely important following engagement of the head in obstructed labor. The interspinous diameter (approximately >10 cm) usually is the smallest diameter of the pelvis.

Plane of the pelvic outlet: This consists of 2 triangular areas created from the connection of an imaginary line between the 2 ischial tuberosities. The apex of the posterior triangle is at the tip of the sacrum, and the apex of the anterior triangle is under the pubic arch. The following 3 diameters of the outlet are of importance:

• Anteroposterior diameter: This normally is 9.5-11.5 cm and extends from the lower margin of the symphysis pubis to the tip of the sacrum.

·         Transverse diameter: This commonly is 11 cm and is the distance between the inner edges of the ischial tuberosities.

·         Posterior sagittal diameter: This usually exceeds 7 cm and extends from the tip of the sacrum to a right-angle intersection with the line between the ischial tuberosities.

Relevant terminology

Engagement: This occurs when the biparietal diameter in a vertex position passes through the plane of the pelvic inlet. This generally is achieved when the leading bony point of the skull has reached the level of the ischial spines.

Position: This describes the relationship of the fetal presenting part with the maternal pelvis.

Asynclitism: The fetal head accommodates the transverse axis of the pelvic inlet, but the sagittal suture (while remaining parallel to the transverse axis) may be deflected anteriorly or posteriorly and therefore is not exactly between the sacral promontory and symphysis pubis. This is called asynclitism. It can be defined as an anterior or posterior asynclitism.

• For cephalic presentations, the reference point is the occiput, whereas in breech presentations, the reference point is the sacrum.

·         Position is always described in reference to the maternal right or left side of the pelvis.

·         Determination of the position is crucial in forceps application and traction. The fontanelles and sutures are used to determine the position. The finding that the fontanelles are not easily palpable is not uncommon; this occurs because of distortion, molding, or caput formation.

·         The position can be determined by finding the location of the sagittal suture and its relationship to the posterior portion of the ear, if palpable. If the sagittal suture is in a U formation, an anterior asynclitism presentation often occurs (ie, presentation of the anterior parietal bone of the fetal head). Conversely, if the sagittal suture is in the shape of an inverted U, this may indicate posterior asynclitism (ie, posterior parietal bone) presentation.

·         Most fetuses can be delivered by forceps if they are in or can be maneuvered (manually or by forceps) into an occiput anterior or posterior position.

·         Correct determination of the position may be the most important step prior to forceps application.

·         Presentation: This is the relationship between the leading fetal part and the maternal pelvic inlet (eg, cephalic, breech, shoulder).

·         Lie: This is the relationship between the fetal longitudinal axis and the maternal longitudinal axis (eg, longitudinal, oblique, transverse).

Contraindications: The following are contraindications to forceps-assisted vaginal deliveries:

• Any contraindication to vaginal delivery .

·         Refusal of the patient to consent to the procedure

·         Cervix not fully dilated or retracted

·         Inability to determine the presentation and fetal head position or pelvic adequacy

·         Suspected cephalopelvic disproportion

·         Unsuccessful trial of vacuum extraction

·         Absence of adequate anesthesia

·         Inadequate facilities and support staff

·         Inexperienced operator

Imaging Studies:

• The decision for forceps delivery is made in the second stage of labor, when delivery of the fetus is only minutes away. Time pressure frequently is present. Therefore, the use of imaging studies at this time usually is too time-consuming and not helpful.

• X-ray pelvimetry and pelvic MRI and CT scan have been shown to be helpful in defining the pelvic anatomy.

• Ultrasound evaluation of the fetus also is important in gathering information to help with the forceps delivery. This tool could also be used at the time of forceps application to differentiate between an occiput-posterior versus an occiput-anterior presentation.

• All the studies mentioned can be performed in a timely fashion when indicated, but none of them is a specific test for forceps delivery.

Preoperative details: Reviewing the indications for operative vaginal delivery and confirming the presence of all the prerequisites of forceps application are crucial steps. Forceps procedures frequently need to be performed emergently. Therefore, all the pros, cons, risks, benefits, and alternatives of the procedure should be discussed with the patient, and her consent should be obtained, in advance when possible. All of the above should be documented in detail.

The type of forceps to be used depends on the specific indications and conditions. The most commonly used forceps is the Simpson forceps, which is used to deliver a molded fetal head, as is commonly seen in nulliparous women. Also used commonly is the Tucker-McLane forceps, which has a more rounded cephalic curve, more suitable for the unmolded fetal heads commonly seen in multiparous women. Many providers now use the Simpson forceps with the Luikhart modification (semifenestrated).

The decision of what type of anesthesia should be used should be made before the application of forceps. An adequate level of anesthesia should be in effect before attempting forceps delivery. Although reports have been published that suggest using only local infiltration anesthesia to the perineal body, the authors believe that this type of anesthesia is far less than adequate except in dire emergency situations. The minimum anesthesia for forceps delivery should be a pudendal block plus local infiltration anesthesia; this can be further augmented with intravenous sedation. An adequate level of anesthesia puts the patient, the operator, and the support staff at ease in what may be a highly emotionally charged environment of forceps delivery, and it eliminates unnecessary difficulties.

Adequate anesthesia also is achievable with regional or general anesthesia. Regional anesthesia usually is used; general anesthesia usually is reserved for very unusual emergency situations. With the former, the patient should be prepared and draped after the anesthesia has been delivered via epidural or a spinal injection. With the latter, the surgeon should be ready, with the patient properly draped, before administration of general anesthesia.

Visceral sensory fibers from the uterus, cervix, and upper vagina traverse through the Frankenhäuser ganglion (lies just lateral to cervix), and, after parting the pelvic and iliac plexuses, they enter the spinal cord through the X, XI, and XII thoracic nerves and the first lumbar nerves. A good and acceptable level of regional anesthesia usually is achievable with pudendal, low spinal, or epidural regional anesthesia.

The bladder should be catheterized and emptied in preparation for forceps operative deliveries, regardless of type of anesthesia used.

Intraoperative details:

Application of the forceps

The most crucial point of forceps delivery is the precise knowledge of the presentation and the fetal head position. The term pelvic application is used when the left blade is applied to the left side of the pelvis and the right blade is applied to the right side of the pelvis. Pelvic application alone may be injurious to the fetus and mother.

Of importance is to reemphasize the fact that an operator should be present who knows when to stop, to not force the issue, and to not aggressively use both forceps and vacuum in combination.

Application technique

See for a brief explanation of a simple outlet forceps delivery for an occiput-anterior position.  

After ensuring proper anesthesia and an empty bladder, the fetal head, the maternal pelvic sidewalls, and the forceps instrument should be lubricated.

The presence of the sagittal suture in the anteroposterior diameter of the pelvic outlet is confirmed, and the left blade is introduced initially into the left side of the pelvis and guided to the appropriate position along the fetal head. The left blade is left in place to stand freely or is held in place without pressure by an assistant. The right blade is introduced into the right side of the pelvis in the same fashion.

At all times, attention should be given to avoiding the use of force. The blades should be held like a pencil, almost in a vertical position, and, as they are introduced without force into the vagina, they are brought to a horizontal position. The fingers in the vagina should only guide the blades and should not apply pressure on or displace the fetal head.

After proper placement of the left blade, it should lie almost parallel to the floor. With insertion of the right blade, the forceps should lock without pressure.

Appropriateness of application

In a true occiput anterior position, the long axis of the blades corresponds to the occipitomeatal diameter, with the tips of the blades lying over the cheeks; the blades should lie evenly against the sides of the head. Ideally, the sagittal suture of the fetal head will be in the middle, and the blades will be equidistant from the sagittal suture. Also, at all times, the fontanelles (if palpable) should remain in between the blades and should not be covered by them. The forceps should lock easily without any force and stand parallel to the plane of the floor. The appropriateness of application should be confirmed before applying traction.

Traction with forceps and episiotomy

Traction always should be applied intermittently, and the head should be allowed to recede between contractions, as in a spontaneous delivery, with the exception of emergency deliveries.

After confirming proper forceps application, traction starts parallel to the plane of horizon and then is elevated to an almost vertical position as the fetal head prepares for its extension. The amount of traction should be the least necessary to accomplish safe fetal head descent. This traction pressure should not exceed 45 pounds in primiparas and 30 pounds in multiparas. The tractive and compressive forces are not a contest of muscle strength. Application of proper force comes with thoughtfulness, experience, and finesse in following the paths of least resistance. Knowing when to stop and abandon the procedure is a matter of experience. Assuming that one has done everything according to proper protocols and no progress is observable in 3 traction attempts, operative vaginal delivery should be discontinued and preparation for abdominal delivery should start as soon as possible.

An episiotomy should be performed when the perineum is distended properly. Although controversy exists regarding the type of preferred episiotomy, many obstetricians use a mediolateral episiotomy for operative vaginal deliveries in an attempt to protect the rectum and rectal sphincter from injury. However, this is associated with more pain with healing.

Postoperative details: After forceps delivery, a detailed examination of the maternal pelvis and a rectal examination are essential to help diagnose and treat hidden lacerations. The newborn also should be carefully examined.

A high index of suspicion is necessary to help diagnose and treat the complications of operative vaginal deliveries. Severe and painful edema of the vulvovaginal area is common in these patients. Along with other injuries, this can make spontaneous voiding difficult, in which case an indwelling catheter should be placed. Proper postoperative pain control is essential. These patients are at increased risk for hemorrhage, and a postoperative hemogram should be obtained and the condition corrected as needed.

Before discharge, pelvic and rectal examinations may help confirm the integrity of pelvic organs and may exclude such entities as pelvic hematoma, rectal tears, and misplaced sutures. Diagnostic studies should be ordered as needed.

Follow-up care: In the absence of specific forceps-related complications, a follow-up postpartum examination within 4-6 weeks, with a thorough pelvic examination, usually is sufficient.

Research into possible forceps delivery complications is hampered by a number of potential biases, including the level of experience of the operators, the small number of patients studied under similar circumstances, changes in practice and definitions, and the inability to achieve statistical power to answer relevant questions. Maternal and fetal complications have been reported to vary in their severity and are related inversely to the skill and judgment of the operator. The following are complications associated with forceps-assisted vaginal deliveries:

• Maternal complications
• Early (ie, acute) complications include (1) lacerations to the cervix, vagina, perineum, or bladder; (2) extension of episiotomies; (3) increase in blood loss; (4) hematomas; and (5) intrapartum rupture of the unscarred uterus.

o        Late complications mainly are related to injury to the pelvic support tissues and organs and include (1) urinary stress incontinence, (2) fecal incontinence, (3), anal sphincter injuries, and (4) pelvic organ prolapse.

·         Fetal complications

• Transient facial forceps marks, bruising, lacerations, and cephalohematomas are possible.

o        Skull fractures, intracranial hemorrhage with falx, or tentorial lacerations also have been reported.

o        Cerebral palsy, mental retardation, and behavioral problems tend to be more related to hypoxic episodes or other intrapartum, environmental, or congenital factors.