Chapter 110

The Emergency Physician will, on occasion, be required to handle the delivery of an infant when an Obstetrician or Family Physician is not available. The management of normal labor and delivery requires a basic understanding of the mechanisms of labor, the assessment and treatment of the mother, the safe delivery of the infant, and careful observation of both in the immediate postpartum period.

Labor is defined as repetitive uterine contractions leading to cervical change (dilation and effacement). The mechanisms of labor, also known as the 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 ultimate goal of labor.

### Pelvic Anatomy

The success of a vaginal delivery depends on the four P’s (presentation, position, place of the fetus, and adequacy of the pelvis). The physician must be able to assess the mother in anticipation of potential problems. The most commonly measured planes of the maternal pelvis are the pelvic inlet and the midplane. The two measurements most clinically useful are the diagonal conjugate and the ischial interspinous or bi-ischial diameter (Figure 110-1). The diagonal conjugate refers to the distance from the inferior border of the pubic symphysis to the sacral promontory (Figure 110-1A). Place the tip of the middle finger at the sacral promontory and note the point on the hand that contacts the pubic symphysis (Figure 110-1B). Measure this distance as the diagonal conjugate. The diagonal conjugate is generally 1.5 to 2 cm longer than the obstetric conjugate. The average measurement of the anteroposterior diameter of the pelvic inlet is 12.5 cm, with the critical distance being 10 centimeters. Therefore, the critical distance to keep in mind when measuring the diagonal conjugate is 8.5 centimeters. Measure the ischial interspinous diameter. Palpate the ischial tuberosities and measure the distance between them (Figure 110-1C). A value greater than 8 cm is considered adequate. Distances less than these represent potential problems that may result in fetal entrapment, shoulder dystocia, or prolonged labor. It is not often feasible to take these measurements in the Emergency Department as the patient is often delivering precipitously.

###### Figure 110-1

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.

### True Labor versus False Labor

False labor is common in late pregnancy. It is characterized by contractions that are brief, occur at irregular intervals, and whose intensity remains the same. These are often referred to as Braxton-Hicks contractions. These contractions primarily cause discomfort in the lower abdomen. Physical examination often reveals the fetus has not descended and the cervix is not dilated. False labor ...

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