General pathology · Paediatric pathology
Prematurity and fetal growth restriction !
- Topic
Being born too early or growing too little in the womb leaves organs immature or without reserves, and explains much of newborn disease.
Updated 2026-11-01
What it is
Preterm birth happens before 37 completed weeks of gestation; fetal growth restriction is the failure of a fetus to reach its growth potential. They are different problems that often coincide. Complications of preterm birth are the leading cause of death in children under five worldwide, according to WHO.
Step by step
- The placenta fails to supply enough oxygen and nutrients (preeclampsia, hypertension, smoking, maternal malnutrition).
- The fetus redirects blood to the brain, heart and adrenals, at the expense of viscera, muscle and skin.
- The head keeps growing, but the liver stores little glycogen and there is little fat: the abdomen is small.
- Lower renal blood flow means less fetal urine, and oligohydramnios appears.
- At birth, with no reserves, the baby tends towards hypoglycaemia, hypothermia and polycythaemia.
- In the long run, fetal growth restriction is linked to higher cardiovascular and metabolic risk in adulthood.
Symmetric and asymmetric fetal growth restriction
| Feature | Symmetric | Asymmetric |
|---|---|---|
| Onset | Early in gestation | Third trimester |
| Typical cause | Fetal: chromosome disorders, congenital infections, toxins | Placental or maternal: preeclampsia, hypertension, smoking |
| Proportions | Head, length and weight equally reduced | Weight reduced with the head relatively spared |
| Outlook | Worse; depends on the cause | Better if the cause is corrected or delivery is timed well |
Clinical notes
- Immature lung: respiratory distress syndrome from lack of surfactant; later bronchopulmonary dysplasia.
- Brain: germinal matrix and intraventricular haemorrhage, especially in the very preterm; periventricular leukomalacia.
- Gut: necrotising enterocolitis; eye: retinopathy of prematurity; heart: patent ductus arteriosus.
- Immature immunity and invasive procedures: neonatal sepsis; immature breathing control: apnoea of prematurity.
Test yourself
Think of the answer, then tap the question to see it.
Which type of growth restriction does third-trimester placental insufficiency cause?
Asymmetric: the fetus spares head growth and cuts back on viscera and fat.
Why does a growth-restricted newborn tend towards hypoglycaemia?
Because it has little liver glycogen and little fat, so few reserves to keep glucose up after birth.
Which brain complication is typical of the extremely preterm infant?
Germinal matrix haemorrhage, which can extend into the ventricles.
Before which gestational age is a birth considered preterm?
Before 37 completed weeks of gestation.
Related
- Neonatal respiratory distress syndrome: surfactant and hyaline membranes
- Necrotizing enterocolitis: why the premature gut is vulnerable
- Sudden infant death syndrome: what is known
- Multifactorial (complex) disorders
Related conditions
- Prematurity and its complications
- Fetal growth restriction
- Neonatal respiratory distress syndrome (hyaline membrane disease)
- Necrotising enterocolitis
- Intraventricular haemorrhage of prematurity
- Bronchopulmonary dysplasia
- Retinopathy of prematurity
- Patent ductus arteriosus
- Apnoea of prematurity
- Neonatal hypoglycaemia (including infant of a diabetic mother)
- Neonatal sepsis
- Preeclampsia
- Premature rupture of membranes (PROM and PPROM)
Elsewhere in DurgiPedia
- Fetal growth and growth restriction
- Fetal lung, kidney and brain maturation: what preterm birth interrupts
- Abnormal placentation: previa and the accreta spectrum
- Newborn physiology and fetal maturation
- Fetal circulation and the transition at birth
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Preterm birth (World Health Organization, 2026); Intrauterine growth restriction: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026).
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Representative model, for educational purposes only.