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.
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.
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 ...