Unit
- Preterm birth definition: A birth occurring before 37 completed weeks of gestation. The World Health Organization categorizes preterm birth into extremely preterm (less than 28 weeks), very preterm (28 to 32 weeks), and moderate to late preterm (32 to 37 weeks). These classifications guide clinical care intensity and resource allocation.
- Gestational age assessment: Accurate dating via last menstrual period and early ultrasound is essential for determining prematurity. Newborn physical examination using the Ballard Score provides a quick postnatal estimate when prenatal dates are uncertain.
- Birth weight categories: Low birth weight (below 2500 grams), very low birth weight (below 1500 grams), and extremely low birth weight (below 1000 grams) correlate with morbidity and mortality risk. Small for gestational age infants face additional metabolic and growth challenges.
- Incidence and global variation: Preterm birth rates range from 5% in some European countries to 18% in parts of Sub-Saharan Africa and South Asia. Socioeconomic factors, maternal health access, and multiple gestation rates drive these differences.
- Causes of preterm labor: Approximately 40% of preterm births are spontaneous with unknown etiology; others are iatrogenic or linked to infection, placental abruption, cervical insufficiency, and maternal chronic conditions like hypertension.
- Impact on organ systems: The degree of immaturity affects nearly every organ. The lungs lack surfactant, the brain is hemorrhagic-prone, temperature regulation is poor, and immune defenses are underdeveloped. These vulnerabilities drive NICU management protocols.
- Classification by birth weight vs. gestational age: Both metrics are used together because they independently predict outcomes. For example, a very low birth weight infant at 30 weeks may have different risks than an extremely low birth weight infant at 27 weeks.
- Clinical utility of classifications: Standardized definitions enable consistent research, benchmarking across NICUs, and communication among care teams. Administrative staff use these categories for resource planning and assignment of acuity levels.
- Thermoregulation challenges: Preterm infants have a high surface area to volume ratio, limited brown fat, and immature skin leading to rapid heat loss. Maintaining a neutral thermal environment is critical; incubators, radiant warmers, and skin-to-skin contact help prevent hypothermia and its metabolic consequences.
- Respiratory distress syndrome: Surfactant deficiency causes alveolar collapse, leading to hypoxemia and work of breathing. Treatment includes exogenous surfactant administration and respiratory support via nasal CPAP or mechanical ventilation. Antenatal corticosteroids reduce risk when given before preterm birth.
- Feeding and nutrition: Immature suck-swallow-breathe coordination often requires gavage feeding initially. Early trophic feeds with breast milk stimulate gut maturation and reduce necrotizing enterocolitis risk. Parenteral nutrition may be needed to meet high metabolic demands until full enteral feeds are tolerated.
- Infection susceptibility: Immature innate and adaptive immunity increases vulnerability to sepsis. Routine practices include hand hygiene, minimal handling, and strict line care. Prophylactic antibiotics are used in settings with high risk, and early recognition of signs is vital due to subtle presentations.
Terminology
- Preterm birth
- Delivery before 37 weeks of gestation.
- Extremely preterm
- Birth before 28 weeks of gestation.
- Very preterm
- Birth between 28 and 32 weeks.
- Late preterm
- Birth between 34 and 36 weeks, 6 days.
- Small for gestational age
- Birth weight below the 10th percentile for gestational age.
Quick Revision
- Preterm birth is defined as delivery before 37 weeks and is subclassified by gestational age and birth weight.
- Accurate gestational dating and birth weight classification are critical for risk stratification and clinical management.
- Global incidence varies; prematurity is a leading cause of neonatal morbidity and mortality worldwide.
- Understanding these definitions helps healthcare administrators allocate resources and design appropriate care pathways.