Emergency Physicians must be prepared to manage the precipitous delivery of a newborn. It is a rare occurrence and requires a good amount of preparation. The Emergency Department is not the ideal environment in which to deliver a newborn.1 A Labor and Delivery suite with a specialist trained in handling potential complications (e.g., malpresentation, prematurity, or prolapsed cord) is preferred. The Emergency Physician will need to deliver the infant when transfer to a facility with a trained Obstetrician, Family Physician, or Certified Nurse Midwife is not feasible.2 A thorough understanding of the physiology of pregnancy and labor, the evaluation of the pregnant female, and the proper technique of delivery will help to ensure the safety of both mother and fetus.
Labor involves the repetitive uterine contractions that lead to cervical changes (i.e., dilation and effacement). The mechanisms of labor, or cardinal movements of labor, describe the changes in the position of the fetal head as it travels through the birth canal. The safe delivery of the infant is the goal of labor while decreasing maternal morbidity.
ANATOMY AND PATHOPHYSIOLOGY
A successful vaginal delivery depends on the adequacy of the female pelvis. Pelvimetry may be used during prenatal visits to evaluate the adequacy of the pelvic space for fetal passage. Inadequate space may result in fetal entrapment, prolonged labor, and shoulder dystocia.3 The most useful planes for measurement are the pelvic inlet and the midplane (Figures 162-1A and 162-1B). The pelvic inlet is through measurement of the diagonal conjugate. The midplane is through measurement of the ischial interspinous or bi-ischial diameter.3
Measure pelvic distances to determine if there may be difficulties during the delivery. A. The pelvic conjugate diameters. B. Measuring the diagonal conjugate. C. The ischial interspinous distance.
The diagonal conjugate refers to the distance from the inferior border of the pubic symphysis to the sacral promontory (Figure 162-1A). The normal diagonal conjugate measures approximately 12.5 cm, with the critical distance being 10 cm. Place the tip of the middle finger at the sacral promontory and note the point on the hand that contacts the pubic symphysis (Figure 162-1B). The true conjugate, a radiographic measurement of the pelvic inlet, represents the smallest diameter of the inlet from the sacral promontory to the superior aspect of the pubic symphysis (Figure 162-1A). It can be estimated by subtracting 1.5 to 2 cm from the diagonal conjugate and normally measures 11 cm or more (Figure 162-1A). The obstetric conjugate is the distance from the sacral promontory to a point on the inner surface of the pubic symphysis that is a few millimeters from the upper margin of the pubic symphysis (Figure 162-1A). This corresponds with the true conjugate and ...