High-risk pregnancy series: an expert’s viewThe management of preterm labor☆
Section snippets
Prematurity
A preterm delivery, as defined by the World Health Organization, is one that occurs at less than 37 and more than 20 weeks’ gestational age. In the United States, the preterm delivery rate is approximately 11%, whereas in Europe it varies between 5% and 7%. In spite of advances in obstetric care, the rate of prematurity has not decreased over the past 40 years. In fact, in most industrialized countries it has increased slightly (Figure 1). Prematurity remains a leading cause of neonatal
Preterm labor
Preterm labor is usually defined as regular contractions accompanied by cervical change occurring at less than 37 weeks’ gestation. Spontaneous preterm labor accounts for 40–50% of all preterm deliveries, with the remainder resulting from preterm premature rupture of membranes (PROM) (25–40%) and obstetrically indicated preterm delivery (20–25%).3 In this article I will deal only with the management of preterm labor.
The pathogenesis of preterm labor is not well understood, and it is often not
Infection and preterm birth
There is a growing body of evidence that infection of the decidua, fetal membranes, and amniotic fluid is associated with preterm delivery.4 Clinical chorioamnionitis complicates 1–5% of term pregnancies, but nearly 25% of preterm deliveries. In a study by Guzick and Winn,5 histological chorioamnionitis was more common in preterm deliveries than in term ones (32.8% versus 10%). Watts et al6 investigated patients in preterm labor and demonstrated that positive amniotic fluid cultures were
Risk factors
In the United States, race is a significant risk factor for preterm delivery. Black women have a prematurity rate of about 16–18%, compared to 7–9% for white women. Women younger than 17 and older than 35 carry a higher risk of preterm delivery. Less education and lower socioeconomic status are also risk factors, although they probably are not independent of one other. The relative contribution of various causes of preterm birth differs by ethnic group. For example, preterm labor more commonly
Prevention
Conceptually, prevention of preterm labor may be divided into two major areas. The first involves a reduction in the presence of one or more of the specific risk factors described above or, in a more general approach, an improvement in quality of life including income and nutritional enhancement, and a reduction in physical and emotional stress. Although space does not permit a thorough review of these attempts, suffice it to say that in developed countries these approaches have not
Treatment
The therapeutic interventions considered in the setting of preterm labor generally have the following goals: 1) to inhibit or reduce the strength and frequency of contractions, thus delaying the time to delivery, and 2) to optimize fetal status before preterm delivery. In this section, many of the contemporary obstetric therapeutic strategies proposed to achieve these goals are reviewed.
Antibiotics
Preterm labor, especially at less than 30 weeks’ gestation, has been associated with occult upper genital tract infection (Figure 2). Many, if not all, of the bacterial species involved in this occult infection are capable of inciting an inflammatory response, which ultimately may culminate in preterm labor and delivery. Antibiotics therefore have the potential to prevent and/or treat spontaneous preterm labor. Elder et al70 were among the first investigators to study the use of antibiotics to
Group B streptococcus
Group B streptococcus is an important cause of neonatal morbidity and death, especially in premature infants, but its role in the initiation of preterm labor is uncertain. Approximately 10–20% of US women are group B streptococcus positive during pregnancy. The risk of preterm birth appears to be greatest in women with group B streptococcus in the urine, perhaps indicating a greater degree of colonization; thus treatment of the urinary tract infection may result in a reduction in preterm birth.
Corticosteroids
The use of antenatal corticosteroids for the prevention of neonatal respiratory distress syndrome stems from the animal work by Liggins and Howie in the late 1960s.90 They observed that gravid sheep, which had received glucocorticoids to induce preterm labor, gave birth to lambs that had accelerated fetal lung maturity and decreased respiratory problems at birth. After this observation, these investigators conducted the first trial of antenatal glucocorticoid therapy in humans and found that 12
Delivery
The remarkable reduction in neonatal mortality that has occurred in the last several decades is mostly due to the widespread use of newborn intensive care for preterm newborns. Birth in close proximity to a newborn intensive care unit with an experienced resuscitation team in attendance is one of the best predictors of neonatal survival. Obstetricians and other delivery attendants should do all in their power to insure that each preterm newborn can benefit from this technology.
Women in preterm
Summary
The epidemiology, pathophysiology, and current therapeutic strategies utilized in the setting of preterm labor have been reviewed. Despite our best efforts, preterm delivery remains a significant clinical problem, accounting for a substantial component of all neonatal morbidity and mortality. Although we have gained important insights into the pathophysiology of preterm labor over the past several decades, effective therapeutic interventions to decrease spontaneous preterm delivery have not
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This work is based in part on a literature review performed by Patrick Ramsey, MD, and his contribution is acknowledged.
We would like to thank the following individuals who, in addition to members of our Editorial Board, will serve as referees for this series: Dwight P. Cruikshank, MD, Ronald S. Gibbs, MD, Gary D. V. Hankins, MD, Philip B. Mead, MD, Kenneth L. Noller, MD, Catherine Y. Spong, MD, and Edward E. Wallach, MD.