The precise incidence of operative vaginal delivery in the United States is unknown. According to the National Vital Statistics Report, forceps or vacuum delivery was coded on the birth certificate as the method of delivery for 4.5 percent of vaginal births in the United States in 2006 (Martin and colleagues, 2009).
True forceps were first devised in the late 16th or beginning of the 17th century. The reader is referred to the 19th and earlier editions of Williams Obstetrics regarding their history.
These instruments basically consist of two crossing branches. Each branch has four components: blade, shank, lock, and handle. Each blade has two curves: The cephalic curve conforms to the shape of the fetal head, and the pelvic curve corresponds more or less to the axis of the birth canal (Fig. 23-1). Some varieties are fenestrated or pseudofenestrated to permit a firmer grasp of the fetal head.
Tucker–McLane forceps. The blade is solid and the shank is narrow.
The blades are connected to the handles by the shanks. The common method of articulation, the English lock, consists of a socket located on the shank at the junction with the handle, into which fits a socket similarly located on the opposite shank (Figs. 23-1 and 23-2). A sliding lock is used in some forceps, such as Kielland forceps (Fig. 23-3).
Simpson forceps. A. Note the ample pelvic curve in the blades. B. The cephalic curve is evident in the articulated blades. The fenestrated blade and the wide shank in front of the English-style lock characterize the Simpson forceps.
Kielland forceps. The characteristic features are the sliding lock, minimal pelvic curvature, and light weight.
Classification of Forceps Deliveries
The current classification of the American College of Obstetricians and Gynecologists (2000, 2002) for forceps and vacuum operations is summarized in Table 23-1. It emphasizes the two most important discriminators of risk for both mother and infant: station and rotation. Station is measured in centimeters, −5 to 0 to +5. Deliveries are categorized as outlet, low, and midpelvic procedures. High forceps in which instruments are applied above 0 station have no place in contemporary obstetrics.
Table 23-1. Classification of Forceps Delivery According to Station and Rotationa |Favorite Table|Download (.pdf)
Table 23-1. Classification of Forceps Delivery According to Station and Rotationa
Scalp is visible at the introitus without separating the labia
Fetal skull has reached pelvic floor
Sagittal suture is ...