In the two prior editions of this textbook, forceps delivery and vacuum extraction were covered in separate chapters. Following the lead of Williams Obstetrics (Cunningham, 2014), the two topics have been combined under the heading operative vaginal delivery (OVD) for this third edition. Although overall rates for OVD are declining in the United States, the need is urgent for increased training in and use of these procedures as one method of curbing the escalating cesarean delivery rate (Spong, 2012). This chapter presents a structured approach to resident training in OVD procedures. As a second goal, the technical considerations involved in the use of various types of forceps and vacuum extractors are emphasized.
Forceps have been used for more than four centuries, whereas vacuum extractors date back only 60 years. The first crude forceps, which are Chamberlen forceps, have been modified in small and large ways over the centuries. The first meaningful modification of the original instrument was the addition of a pelvic curve, variably credited to Levret of France or Smellie of England in the mid 18th century. To best appreciate the pelvic curve, one must view the forceps from the side as they rest on a flat surface (Fig. 23-1). The toes of the blades are elevated relative to the shanks. This corresponds to the axis of the pelvis, referred to as the curve of Carus.
Tucker-McLane forceps, side view. Anatomy of the blade is labeled.
The second major advance was the enunciation of the principle of axis traction by the French obstetrician Tarnier in 1877. Simply stated, the higher the station of the fetal head at forceps application, the more posterior the vector of initial traction should be. This concept is illustrated in Figure 23-2, which shows the need to gradually elevate the forceps handles as the head descends. As a teaching tool for this point, an American obstetrician, Arthur Bill, developed an axis traction device, which can be placed over the finger guards of most forceps (Fig. 23-3A). The instrument has a T-shaped handle, with a laterally placed indicator arrow and line (Fig. 23-3B). When the arrow points directly to the line, traction is along the path of least resistance. This device is a valuable training aid. For the neophyte, it shows the starting and finishing positions of the forceps handles and the arc that they transcribe as the head descends.
The higher the fetal head, the more posterior is the initial direction of traction. Of equal importance, the vector of traction must change continuously as the head descends, becoming progressively more anterior.
A. Bill axis traction device. The arms to the right ...