Chapter 22: Preterm Labor, Labor and Delivery

LEARNING OBJECTIVES

1. Describe criteria used for the diagnosis of preterm labor, labor, and abnormal labor.

2. Explain the physiology of labor and the pathophysiology of preterm labor.

3. Understand appropriate pharmacologic and nonpharmacologic therapies in the management of labor and induction of labor.

4. Compare and contrast commonly used tocolytics for the treatment of preterm labor.

5. Define common causes and treatments for postpartum hemorrhage.

INTRODUCTION

Labor is the physiologic process by which the fetus and placenta are expelled from the uterus. Labor is defined as the presence of uterine contractions of sufficient intensity, frequency, and duration to bring about demonstrable effacement (thinning) and dilatation of the cervix.¹ It involves a complex interaction of maternal, fetal, and placental signals. These complicated endocrine, paracrine, and autocrine mechanisms have been shown to be different among different species. In humans, all of the mechanisms responsible for labor have not been completely elucidated, but the timing of delivery appears to be determined by the placenta and increasing levels of corticotropin-releasing hormone.¹

Parturition, or giving birth, has been divided into four cervical and uterine phases corresponding to the physiologic changes that occur during pregnancy.¹ Although the uterus and cervix are part of the same organ, they respond differently during pregnancy. The uterus transitions from a state of relative quiescence, or rest, to activation of the myometrium in preparing for labor, followed by the actual process of labor and eventually recovery.¹ The cervix performs its transformation early in pregnancy, beginning by softening within the first month, and slowly progresses to cervical ripening during the last weeks of the pregnancy. This is followed by dilatation during labor and concludes with repair and remodeling during the postpartum period while the uterus is undergoing involution, the continued uterine contraction which compresses uterine blood vessels to prevent postpartum hemorrhage.¹

In this chapter, we will examine the physiology of labor and the appropriate pharmacologic and nonpharmacologic therapies in the management of labor and induction of labor. In addition, the pathophysiology of preterm labor will be reviewed, including discussion of preventative therapies and the commonly used tocolytics for the treatment of preterm labor. Finally, the common causes and treatments for postpartum hemorrhage will be summarized.