Premature Birth refers to birth occurring before 37 completed weeks of pregnancy. It is also called preterm birth in clinical terminology, although the supplied term emphasises the same concept. Prematurity is commonly subdivided by gestational age because the degree of immaturity strongly influences neonatal risk. Extremely preterm birth occurs at the earliest gestations, very preterm birth occurs at intermediate early gestations, and moderate-to-late preterm birth occurs closer to term.
The exact gestational-age boundaries used for these categories can vary slightly between organisations. Premature Birth can be spontaneous, resulting from spontaneous labour or premature rupture of membranes, or medically indicated, when delivery is recommended because continuing pregnancy poses greater maternal or fetal risk. Important causes of medically indicated preterm delivery include Pre-eclampsia, fetal growth restriction and significant Placental Disorders. Prematurity is a major contributor to neonatal morbidity and mortality because organ systems, especially the lungs, brain, gastrointestinal tract and immune system, continue to mature throughout late pregnancy.
Spontaneous Premature Birth can result from several interacting pathways rather than one single cause. These include infection or inflammation of the reproductive tract and membranes, cervical insufficiency, uterine overdistension, placental bleeding, maternal systemic disease and premature rupture of membranes. Multiple pregnancy substantially increases risk because uterine distension and placental or cervical factors differ from singleton pregnancy. Previous spontaneous preterm birth is one of the strongest clinical predictors of recurrence.
Short cervical length measured by transvaginal ultrasound can also identify increased risk in selected pregnancies. Some cases occur despite apparently normal pregnancy and no identifiable trigger. Conversely, some births before 37 weeks are deliberately planned because the fetus or mother is at increasing risk, meaning that spontaneous and medically indicated Premature Birth should not be treated as interchangeable. The distinction matters when evaluating prevention strategies because preventing spontaneous labour is fundamentally different from deciding whether medically indicated early delivery is necessary.
Clinical consequences depend strongly on gestational age, birth weight, fetal condition and neonatal circumstances. The lungs may have insufficient surfactant, increasing the risk of respiratory distress and the need for respiratory support. Immature respiratory control can cause episodes of apnoea, while immature blood vessels and brain tissue increase vulnerability to intraventricular haemorrhage. The immature intestine is susceptible to necrotising enterocolitis, and immature immune defences increase susceptibility to infection.
Premature infants may have difficulty maintaining temperature and coordinating sucking, swallowing and breathing, which can necessitate tube feeding and incubator care. The risk of complications falls substantially as gestational age increases, although moderate-to-late premature infants can still experience feeding, temperature regulation, jaundice and respiratory problems. Long-term outcomes vary widely, with many premature babies developing normally while those born at the earliest gestations have higher risks of neurodevelopmental, respiratory, visual and hearing complications.
Assessment of threatened Premature Birth considers symptoms such as regular uterine contractions, pelvic pressure, back pain, vaginal bleeding and fluid leakage. Examination and ultrasound can determine cervical length and whether the membranes have ruptured. Tests may sometimes assess whether intra-amniotic infection or inflammation is likely, but no single test predicts every premature birth. When membranes rupture before labour, the diagnosis and management pathway differs because infection risk and timing of delivery become central concerns.
Fetal assessment includes monitoring heart rate and ultrasound when indicated. Maternal assessment looks for infection, bleeding, hypertension and other conditions that could require delivery. Accurate gestational dating is essential because the benefit of continuing pregnancy and the benefit of early delivery change rapidly with advancing gestation. Pregnancy dating is usually based on early ultrasound or reliable menstrual information according to local practice.
Prevention of Premature Birth depends on the underlying risk. In people with a previous spontaneous preterm birth or a short cervix, interventions may include vaginal progesterone or cervical cerclage in selected circumstances, depending on clinical history and local guidance. Smoking cessation, appropriate spacing of pregnancies and treatment of relevant infections or maternal disease can also reduce some risks, although spontaneous preterm birth remains incompletely preventable.
When premature birth appears imminent, antenatal corticosteroids can accelerate fetal lung maturation and reduce certain neonatal complications. Magnesium sulfate may be offered at very early gestations for fetal neuroprotection according to gestational-age criteria. Tocolytic medication can sometimes delay labour briefly, allowing time for corticosteroids, magnesium sulfate or transfer to a neonatal unit, but it does not permanently prevent premature birth and is not appropriate in every circumstance. Treatment therefore focuses both on delaying birth when safe and preparing for birth when it cannot safely be prevented.
When Premature Birth is medically indicated, the underlying maternal or fetal condition determines timing. For example, severe Pre-eclampsia may make continuing pregnancy dangerous, while severe fetal growth restriction with abnormal placental blood flow may indicate worsening placental insufficiency. In such circumstances, delaying birth solely to reach term may increase risk. This creates a central principle of obstetric decision-making: prematurity itself carries risk, but remaining in the uterus can also become more dangerous.
Delivery decisions therefore balance gestational age, fetal wellbeing, maternal disease, placental function and the capacity of neonatal services. Transfer to a hospital with appropriate neonatal intensive-care facilities may be arranged when time permits. Antenatal counselling commonly discusses likely respiratory support, feeding requirements, length of hospitalisation and gestational-age-specific complications, while recognising that individual neonatal outcomes cannot be predicted with certainty from gestational age alone.
Premature Birth has major implications for neonatal medicine because survival at very early gestations has improved with advances in antenatal steroids, respiratory support, surfactant therapy, infection management, nutrition and neonatal intensive care. Survival statistics, however, depend on gestational age, birth weight, congenital abnormalities, sex, treatment availability and healthcare setting, so figures from one population should not be treated as universal predictions. Extremely premature infants may require prolonged intensive care and follow-up after discharge.
Respiratory problems can persist because lung development continues after birth, while some children require developmental monitoring during childhood. Prematurity can also affect families through prolonged hospitalisation, travel to specialist centres and emotional and financial pressures. These consequences explain why prevention, accurate risk assessment and coordinated perinatal care remain important even when modern neonatal care can support survival at very low gestations.
Premature Birth is distinct from low birth weight, because a baby can be small for gestational age without being premature and can be premature while having relatively high birth weight. It is also distinct from fetal growth restriction, which describes pathological limitation of fetal growth rather than gestational timing alone.
The term should not be interpreted as meaning that a baby is simply an early version of a term newborn: developmental immaturity affects multiple organ systems and can continue to matter after hospital discharge. At the same time, premature birth is a spectrum rather than a single clinical state, and outcomes vary enormously across gestational ages. Understanding whether birth was spontaneous or medically indicated, whether membranes ruptured early, and whether maternal or placental disease was involved is essential for understanding its cause, recurrence risk and implications for future pregnancies.
