The 'sacral hand wedge': a cause of arrest of descent of the fetal head during vacuum assisted delivery.

During a study of 108 vacuum assisted deliveries, a fetal hand was detected in the pelvic space between the head and maternal sacrum in seven of the procedures. The larger presenting diameters resulting from the compound fetal presentations were reflected in a greater number of pulls and higher traction forces recorded during the deliveries. In all cases, extraction of the hand facilitated the completion of birth without causing serious injury to the fetus or maternal perineum. It is recommended that a digital examination to detect the presence of a fetal hand in the sacral space should become a part of standard vacuum delivery practice.