Forceps- and Vacuum-Assisted Deliveries

CHAPTER 169 Forceps- and Vacuum-Assisted Deliveries



Carol Osborn, Jennifer Bell, Dale A. Patterson


Knowledge and experience with instrument-assisted (forceps or vacuum) delivery are important for all obstetrics providers managing the second stage of labor, particularly if there is an emergency, such as severe fetal or maternal compromise. In unexpected situations the knowledgeable use of an assisted delivery may be lifesaving and help reduce morbidity. Assisted deliveries are also a safe alternative to an operative delivery, as long as criteria and indications are followed. The incidence of assisted delivery is decreasing (especially forceps deliveries), in part because the incidence of cesarean delivery is increasing. Only 6% of all vaginal deliveries were assisted deliveries in the United States in 2002. The safe use of these procedures depends on understanding and clinically establishing the station and position of the vertex. A Cochrane review comparing forceps with vacuum found slightly more deliveries with vacuum, and fewer cesarean sections, less maternal trauma, and less general and regional anesthesia use with vacuum. However, the vacuum extractor was associated with an increase in neonatal cephalhematoma and retinal hemorrhages. Serious neonatal injury was uncommon with either form of assisted delivery or instrument.



Classification


Because of difficulties in estimating engagement and in defining different stations, the American College of Obstetrics and Gynecology (ACOG) defined and reclassified instrumented deliveries. The intention of this reclassification is to improve the safety of assisted deliveries and is discussed in the following sections.



Outlet Forceps or Vacuum



• Fetal skull has reached the pelvic floor.

• Fetal scalp is visible between contractions.

• Sagittal suture is in an anteroposterior diameter (i.e., occipitoanterior [OA], right occipitoanterior [ROA], left occipitoanterior [LOA], occipitoposterior [OP], right occipitoposterior [ROP], or left occipitoposterior [LOP]) that is less than 45 degrees from the midline.


Low Forceps or Vacuum



• Leading edge of the vertex is at +2 or greater station.

• Fetal head at this station fills the hollow of the sacrum.

• Head is not on the pelvic floor.

• Rotations are less than 45 degrees.


Midforceps or Vacuum



• Head is engaged.

• Vertex is higher than +2 station.

• Advisable only in emergency situations.

With the classification change, the term high forceps has been eliminated. High forceps describes application of the forceps before engagement of the vertex. This procedure has no place in modern obstetrics because of unacceptably high morbidity rates. Mid-instrumentation is reserved for providers who are experienced with this application. If an obstetrics provider is uncomfortable with the evaluation or application of forceps, a cesarean section is likely a safer route of delivery.


Before any forceps or vacuum application proceeds, the position and station of the vertex presentation must be determined. First, fetal engagement is verified. By definition, engagement indicates the biparietal diameter has passed the plane of the inlet. Clinically the fetal skull is at or below the ischial spines (i.e., 0 station). Checking the amount of space between the fetal head and the symphysis gives an additional measurement of station (Fig. 169-1).


image

Figure 169-1 A, When the lowermost portion of the fetal head is above the ischial spines, the biparietal diameter of the head is not likely to have passed through the pelvic inlet and therefore is not engaged. B, When the lowermost portion of the fetal head is at or below the ischial spines, it is usually engaged. Exceptions occur when there is considerable molding, caput formation, or both. P, sacral promontory; S, ischial spine.


(Modified from Cunningham FG, MacDonald P, Gant N, et al [eds]: William’s Obstetrics, 19th ed. East Norwalk, Conn., Appleton & Lange, 1993.)


Two things that complicate the clinician’s ability to ensure complete engagement and assess descent are (1) molding, which leads to overestimation of descent or station, and (2) asynclitism or OP presentation, which also leads to overestimation of station. To avoid this miscalculation, the clinician should always confirm that the fetal head fills the sacral hollow. When the vertex fills the sacral hollow there should not be room to admit the fingers of the examining hand.


Position can be difficult to determine, especially if the head has marked caput. The following method helps determine position:


• Anterior fontanelle is shaped like a cross or plus (+) and is usually larger than the posterior fontanelle.

• Posterior fontanelle is shaped like a Y.

• When in doubt, the clinician should find the fetal ears to determine position.

If the position and descent meet criteria for an outlet or low instrumentation, then the provider needs to consider whether to use forceps or a vacuum to assist the delivery. The pros and cons of forceps versus vacuum extraction are described in Box 169-1.



Box 169-1 Forceps versus Vacuum Extraction









Forceps


Pros

Higher rate of successful vaginal delivery

Usually a more rapid delivery (e.g., for fetal distress)

Useful in breech (for the aftercoming head) and face presentations

Useful for rotations if clinician is experienced with these

Cons

Requires significant experience

Increased risk of neonatal craniofacial injuries

Increased risk of intracranial hemorrhage

Requires more maternal anesthesia

Associated with more cervical, vaginal, and perineal lacerations

Vacuum


Pros

Easy to apply

Teaches the clinician to follow the pelvic curve

Allows autorotation from occipitoposterior and occipitotransverse positions

Less force applied to the head

Requires less anesthesia

Results in fewer cervical, vaginal, and perineal lacerations

Easier to learn

Clinician can use if not completely sure of head position

Cons

Difficult to maintain vacuum if head is molded or infant has full head of hair

Pull only with contractions, which increases time needed for successful delivery

Associated with intracranial hemorrhage at a greater rate than spontaneous deliveries

Only useful in vertex presentations

Increased incidence of cephalhematomas and retinal hemorrhage


Indications



Conditions Required for Instrumentation



• Vertex presentation (As noted previously, instrumentation may also be required to deliver the head in breech presentation. However, vertex presentation is required for the usual suction and outlet or low forceps applications.)

• Complete cervical dilatation

• Ruptured membranes

• No known severe cephalopelvic disproportion

• If unsuccessful, willingness to abandon procedure and proceed to cesarean section

• Adequate anesthesia is established


Maternal Indications for Instrument Delivery



• Maternal exhaustion. This is associated with prolonged second-stage pushing. Maternal exhaustion is especially common in the nulliparous labor. The lack of a trained labor companion during the second stage is associated with a longer labor and increased use of instrumentation.

• Lack of maternal cooperation.

• Prolonged second stage or failure to progress. The average second stage is 50 minutes for primiparous patients and 20 minutes for multiparous patients. Regional anesthesia prolongs the second stage by inhibiting the maternal urge to push (Table 169-1).

• Medical conditions for which the strain of the second stage of labor would be deleterious. Examples include cardiac valvular disease, respiratory disease (e.g., active asthma), cerebrovascular disease, toxemia, and chronic hypertension.

TABLE 169-1 Limits of the Duration of the Second Stage of Labor before Intervention















Parity Without Regional Anesthetic With Regional Anesthetic
Nullipara 2 hr 3 hr
Multipara 1 hr 2 hr


Maternal and Fetal Indications for Instrument Delivery



• Relative cephalopelvic disproportion.

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May 14, 2017 | Posted by in GENERAL & FAMILY MEDICINE | Comments Off on Forceps- and Vacuum-Assisted Deliveries

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