Malpresentations

The word malpresentation suggests the possibility of adverse consequences, and malpresentation is often associated with increased risk to both the mother and the fetus.

In contemporary practice, cesarean delivery has become the recommended mode of delivery in the malpresenting fetus.

Generally, factors associated with malpresentation include (1) diminished vertical polarity of the uterine cavity, (2) increased or decreased fetal mobility, (3) obstructed pelvic inlet, (4) fetal malformation, and (5) prematurity.

The fetal lie indicates the orientation of the fetal spine relative to the spine of the mother. The normal fetal lie is longitudinal and by itself does not indicate whether the presentation is cephalic or breech.

Great parity, prematurity, contraction or deformity of the maternal pelvis, and abnormal placentation are the most commonly reported clinical factors associated with abnormal lie.

The sensitivity of Leopold maneuvers for the detection of malpresentation is only 28%, and the positive predictive value was only 24% compared with immediate ultrasound verification.

The ready availability of ultrasound in most clinical settings is of benefit, and its use can obviate the vagaries of the abdominal palpation techniques. In all situations, early diagnosis of malpresentation is of benefit.

Cord prolapse occurs 20 times as often with abnormal lie as it does with a cephalic presentation.

External cephalic version (ECV) is recommended at 36 to 37 weeks to help diminish the risk of adverse outcome.

ECV has been found to be safe and relatively efficacious.

A low transverse (Kerr) uterine incision has many surgical advantages and is generally the preferred approach for cesarean delivery for an abnormal lie (see Chapter 19 ).

In the uncommon case of a transverse or oblique lie with a poorly developed lower uterine segment, when a transverse incision is deemed unfeasible or inadequate, a vertical incision (low vertical or classical) may be a reasonable alternative.

A face presentation is characterized by a longitudinal lie and full extension of the fetal neck and head with the occiput against the upper back ( Fig. 17.1 ). The fetal chin (mentum) is chosen as the point of designation during vaginal examination.

All clinical factors known to increase the general rate of malpresentation have been implicated in face presentation; many infants with a face presentation have malformations.

Face presentation is more often discovered by vaginal examination.

A fetus in a brow presentation occupies a longitudinal axis with a partially deflexed cephalic attitude midway between full flexion and full extension ( Fig. 17.3 ). The frontal bones are the point of designation.

Fewer than 50% of brow presentations are detected before the second stage of labor, and most of the remainder are undiagnosed until delivery.

Most brow presentations convert spontaneously by flexion or further extension to either a vertex or a face presentation and are then managed accordingly.

Whenever an extremity, most commonly an upper extremity, is found prolapsed beside the main presenting fetal part, the situation is referred to as a compound presentation ( Fig. 17.4 ). The combination of an upper extremity and the vertex is the most common.

When intervention is necessary, cesarean delivery appears to be the only safe choice.

Cord prolapse occurs in 11% to 20% of cases, and it is the most frequent complication of this malpresentation.

The prolapsed extremity should not be manipulated. However, it may spontaneously retract as the major presenting part descends.

Cesarean delivery is the only appropriate clinical intervention for cord prolapse and nonreassuring fetal heart rate (FHR) patterns because both version extraction and repositioning the prolapsed extremity are associated with adverse outcome and should be avoided.

Persistent compound presentation with parts other than the vertex and hand in combination in a term-sized infant has a poor prognosis for safe vaginal delivery, and cesarean delivery is usually necessary.