- Clinical science
Preterm labor is defined as regular uterine contractions and cervical changes before 37 weeks of pregnancy. Preterm birth is defined as live birth between 20 0/7 weeks and 36 6/7 weeks of gestation. Approximately half of patients who deliver prematurely are diagnosed with preterm labor. Risk factors include a previous preterm birth, a short cervical length during pregnancy, and multiple gestation. Clinical features include early onset of contractions, premature cervical changes, or premature rupture of membranes. The diagnosis is usually clinical and can be supported by a cervical ultrasound and/or fetal fibronectin detection test. Treatment includes tocolysis, antenatal steroids to improve fetal lung maturity, and magnesium sulfate to provide fetal neuroprotection. Tocolytic agents are used to prolong pregnancy to gain time for steroids and magnesium sulfate to take effect. Complications of the preterm child include intraventricular hemorrhage, respiratory distress syndrome, and necrotizing enterocolitis. Avoidance of modifiable risk factors, management of cervical insufficiency, and vaginal progesterone supplementation can help prevent preterm labor in certain risk groups.
- Preterm labor: Regular uterine contractions with cervical effacement, dilation, or both before 37 weeks gestation.
- Live birth between 20 0/7 weeks and 36 6/7 weeks of gestation
- WHO subcategories
- Extremely preterm (< 28 weeks)
- Very preterm (28 to < 32 weeks)
- Moderate to late preterm (32 to < 37 weeks)
- Complications of preterm birth are the leading cause of death in children < 5 years of age worldwide
- Approximately half of patients who deliver prematurely are diagnosed with preterm labor.
- Preterm birth rate in the US: approx. 12% of all live births
Epidemiological data refers to the US, unless otherwise specified.
The exact pathogenesis of premature labor is not well understood, but it is associated with certain risk factors.
High risk factors
- History of preterm birth
- Multiple gestation
Low risk factors
- Maternal and fetal medical conditions
Lifestyle and environmental factors
- Substance use (e.g., alcohol or drugs)
- Maternal or fetal stress
- Maternal age (< 18 years, > 40 years)
- Exposure to certain environmental pollutants
- Low maternal pre-pregnancy weight
- African-american race
- Regular uterine contractions and associated symptoms of labor
- Cervical dilation ≥ 3 cm, effacement, or both
- Premature rupture of membranes
- Also see “ ” for more information
- Single course of antenatal steroids (IM betamethasone or IM dexamethasone )
Tocolysis: administration of tocolytics to inhibit uterine contractions and prolong pregnancy
- Recommended for up to 48 hours to enable administration of antenatal corticosteroids in preterm labor
- First-line: beta-adrenergic agonists: , NSAIDs, or calcium-channel blockers
- Second-line: Magnesium sulfate
Fetal neuroprotection: Magnesium sulfate
- Indication: if birth < 32 weeks is anticipated
- There is no evidence that bed rest and hydration prolong pregnancy
The general immaturity of premature organ systems leads to various complications in the preterm infant: e.g., immature lungs may develop bronchopulmonary dysplasia and immature central nervous system structures may develop intracranial hemorrhage.
- Neonatal (RDS)
- ROP) (
- NEC) (
- PVL) (
- Neurological disorders (e.g., cerebral palsy, learning disabilities, developmental delays, ADHD)
- Problems of homeostasis: apnea, bradycardia, hypothermia
- Infection and sepsis (e.g., pneumonia)
- Anemia of prematurity: impaired ability to produce adequate erythropoietin (EPO); should be suspected in premature infants with low hemoglobin
Intraventricular hemorrhage (IVH)
- Risk factors
- Usually occurs within 5 days of birth
- Most infants are asymptomatic, but saltatory (over several days) or, more rarely, catastrophic (over minutes to hours) courses are also possible
- Lethargy, hypotonia, irregular respirations, seizures, bulging anterior fontanelle
- Cranial nerve abnormalities (e.g., pupils react sluggishly to light) and changes in eye movement (e.g., roving eye movements)
We list the most important complications. The selection is not exhaustive.
- Mothers should avoid modifiable risk factors (see “Etiology” section above)
- Manage , if present (see “Complications” section in “ ”)
- Vaginal progesterone supplementation