Preterm Labor and Birth

Preterm birth is delivery before 37 completed weeks of gestation. It is a leading cause of neonatal death and of long-term morbidity in surviving children, and it occurs through both spontaneous pathways (preterm labor and preterm prelabor rupture of membranes) and medically indicated early delivery for maternal or fetal conditions.

Definition

Preterm birth is birth before 37 completed weeks (259 days) of gestation; it is commonly subdivided by gestational age into extremely, very, moderate, and late preterm, and by pathway into spontaneous preterm labor, preterm prelabor rupture of membranes, and medically indicated preterm delivery.

Scope

This entry covers the definition and subcategories of preterm birth, the spontaneous and indicated pathways that lead to it, the syndrome model that frames spontaneous preterm labor as the final common result of several mechanisms, and the spectrum of consequences for the preterm infant. It is a reference and educational overview and does not provide tocolytic regimens, gestational thresholds for intervention, or any individualized management guidance.

Core questions

• How is preterm birth defined and subclassified?
• What are the spontaneous and indicated pathways to preterm birth?
• Why is spontaneous preterm birth described as a syndrome rather than a single disease?
• What are the short- and long-term consequences of being born preterm?

Key concepts

• Gestational age at birth
• Spontaneous versus indicated preterm birth
• Preterm prelabor rupture of membranes (PPROM)
• Intrauterine infection and inflammation
• Cervical insufficiency
• Late preterm birth
• Neonatal morbidity of prematurity
• Long-term neurodevelopmental sequelae

Key theories

Preterm birth as a syndrome

Spontaneous preterm labor is conceptualized as the final common pathway of several distinct mechanisms, including intrauterine infection and inflammation, uteroplacental ischemia, uterine overdistension, and cervical insufficiency, rather than a single disease entity.

Mechanisms

Spontaneous preterm birth is best understood as a syndrome: the clinical events of preterm labor or membrane rupture can be triggered by several upstream processes, including intrauterine infection and inflammation, decidual hemorrhage, uteroplacental ischemia, pathological uterine distension (as in multiple gestation), and cervical insufficiency, which converge on premature activation of the parturition pathway (Goldenberg, 2008; Muglia, 2010). Indicated preterm birth, by contrast, is an iatrogenic delivery undertaken because continuing the pregnancy poses a greater risk to mother or fetus, as in severe preeclampsia or fetal compromise. The consequences for the infant arise chiefly from organ immaturity, the severity of which scales with how early birth occurs (Saigal, 2008).

Clinical relevance

Preterm birth is a major driver of neonatal intensive care use and of high-risk pregnancy surveillance, and recognizing signs of preterm labor is part of antenatal assessment. This entry describes how preterm birth is classified and why it matters for maternal-newborn care; it is not a guide to predicting, preventing, or treating preterm labor in any individual, which remains the responsibility of the clinical team following current guidelines.

Epidemiology

Preterm birth complicates roughly one in ten births globally, with substantial variation between regions and populations, and it is the leading cause of death in children under five years of age in many settings. Risk factors include prior preterm birth, multiple gestation, infection, short cervix, extremes of maternal age, low socioeconomic status, and smoking; the majority of preterm births are spontaneous rather than indicated (Goldenberg, 2008).

Evidence & guidelines

Comprehensive narrative reviews in The Lancet and the New England Journal of Medicine frame the epidemiology, mechanisms, and outcomes of preterm birth (Goldenberg, 2008; Muglia, 2010; Saigal, 2008), and standard obstetric texts summarize classification and surveillance (Cunningham et al., 2022).

History

Survival of preterm infants improved dramatically over the twentieth century with the development of neonatal intensive care, surfactant therapy, and antenatal corticosteroids, shifting attention from mortality toward long-term morbidity. The conceptual move from viewing preterm labor as a single event to understanding it as a syndrome with multiple causes, articulated in influential reviews (Goldenberg, 2008; Muglia, 2010), reframed both research and prevention efforts.

Debates

Why has preterm birth been so resistant to prevention?

Because spontaneous preterm birth is a syndrome with heterogeneous causes, interventions that target one pathway may not reduce overall rates, and the enigma of largely unexplained spontaneous preterm birth remains a central challenge.

Key figures

• Robert Goldenberg
• Roberto Romero

Seminal works

• goldenberg-2008
• muglia-2010
• saigal-2008

Frequently asked questions

What counts as a preterm birth?

A preterm birth is delivery before 37 completed weeks of gestation; it is further divided by gestational age (for example late preterm at 34 to under 37 weeks, down to extremely preterm before 28 weeks).

Why is spontaneous preterm birth called a syndrome?

Because the same clinical outcome, early labor or membrane rupture, can result from several different underlying processes such as infection, inflammation, uterine overdistension, and cervical insufficiency, rather than from a single cause (Goldenberg, 2008).