Paediatrics chapters
Prematurity, low birth weight, SGA, LGA and IUGR
Definitions of preterm, low birth weight, SGA, LGA and growth restriction, the causes, how to assess gestational age, the short- and long-term problems of preterm and growth-restricted babies, and their care.
- Preterm is birth before 37 completed weeks; low birth weight is under 2500 g; SGA is weight below the 10th centile for gestation and LGA above the 90th.
- Preterm babies suffer from immaturity of every organ: hypothermia, hypoglycaemia, RDS, apnoea, IVH, NEC, jaundice, infection, PDA, and later ROP, BPD and cerebral palsy.
- Asymmetrical IUGR (head spared; placental insufficiency) usually catches up; symmetrical IUGR (head small too; infection, chromosomal) usually does not.
On this page
Overview
Preterm birth and low birth weight are the biggest causes of neonatal death in Pakistan, where Akbar estimates prematurity at about 11-13% of births and term SGA at 10-25% of newborns. Two different problems produce a small baby:
- Born too early (preterm), and/or
- Grew too little in the womb (small for gestational age, usually from growth restriction).
The two often overlap, but their complications differ, and exam questions test the difference.
Definitions
| Term | Definition |
|---|---|
| Preterm | Live birth before 37 completed weeks from the first day of the last menstrual period |
| Term | 37 to 42 weeks |
| Post-term | After 42 completed weeks |
| Low birth weight (LBW) | Below 2500 g, whatever the gestation |
| Very low birth weight (VLBW) | Below 1500 g |
| Extremely low birth weight (ELBW) | Below 1000 g |
| Small for gestational age (SGA) | Below the 10th centile of weight for gestation, or more than 2 SD below the mean |
| Appropriate for gestational age (AGA) | Between the 10th and 90th centile |
| Large for gestational age (LGA) | Above the 90th centile, or more than 2 SD above the mean |
| IUGR | Failure of the fetus to reach its growth potential; most IUGR babies are SGA |
A low birth weight baby is not always preterm: a term baby of 2 kg is LBW and SGA but not preterm. SGA describes size for gestation; IUGR describes a process of poor growth.
Prematurity
Causes
| Group | Causes |
|---|---|
| Maternal | Malnutrition and anaemia, teenage pregnancy or grand multiparity, pre-eclampsia, chronic illness (diabetes, hypertension, renal and heart disease), infection (UTI, malaria, chorioamnionitis), poverty, smoking, short birth interval |
| Uterine and cervical | Incompetent cervix, bicornuate uterus, uterine fibroids |
| Placental | Placenta praevia, abruption |
| Fetal | Multiple pregnancy, chromosomal disorders, congenital infections, hydrops |
| Other | Preterm prelabour rupture of membranes, polyhydramnios, trauma, iatrogenic (early delivery for maternal or fetal reasons) |
Assessment of gestational age
- Dates and early ultrasound before birth.
- After birth, the New Ballard score adds physical signs (skin, lanugo, plantar creases, breast, eye and ear, genitalia) and neuromuscular signs (posture, square window, arm recoil, popliteal angle, scarf sign, heel to ear). It is accurate to within about 2 weeks and most accurate at 30-42 hours of age.
- Rapid visual signs (Akbar):
| Sign | Preterm | Term |
|---|---|---|
| Sole creases | Absent or only 1-2 anterior creases | Creases over the whole sole |
| Breast nodule | Not palpable (under 34 weeks) or about 3 mm (36 weeks) | 4-10 mm |
| Ear cartilage | Soft, poorly formed, slow recoil | Firm, well formed, instant recoil |
| Scalp hair | Fine and fuzzy | Coarse, separate strands |
| Testes and scrotum | Undescended; few rugae | Fully descended; rugae over the whole scrotum |
For maturity read the soles, breasts, ears, hair and scrotum from top to bottom.
Problems of prematurity
| System | Problem and reason |
|---|---|
| Temperature | Hypothermia: large surface area, little fat and brown fat, no shivering |
| Metabolic | Hypoglycaemia (low glycogen), early hypocalcaemia, metabolic bone disease (low calcium, phosphate and vitamin D) |
| Lungs | Respiratory distress syndrome (surfactant deficiency), apnoea of prematurity, later bronchopulmonary dysplasia |
| Brain | Intraventricular haemorrhage, periventricular leukomalacia |
| Heart | Patent ductus arteriosus, causing heart failure |
| Gut | Poor suck and swallow, reflux and aspiration, necrotising enterocolitis |
| Liver | Prolonged and more severe jaundice; kernicterus at lower bilirubin levels |
| Immunity | Infection: little maternal IgG (crosses mainly in the last trimester), thin skin, lines and tubes |
| Blood | Anaemia of prematurity (low iron stores, short red cell life, blood sampling, vitamin E deficiency) |
| Eyes | Retinopathy of prematurity from abnormal retinal vessel growth, made worse by excess oxygen; can cause blindness |
| Kidneys | Poor concentration, electrolyte imbalance; slower drug clearance (wider dose intervals) |
The preterm baby misses most of the maternal IgG, which crosses the placenta mainly in the last trimester, so infection risk rises steeply with lower gestation.
Long-term problems: cerebral palsy (especially after IVH and PVL), post-haemorrhagic hydrocephalus, learning difficulties, deafness, visual problems, chronic lung disease and poor growth. Akbar notes that 5-10% of babies under 1500 g have a major handicap.
Apnoea of prematurity
- Apnoea: breathing stops for more than 20 seconds in a preterm baby (more than 15 seconds in a term baby), or for any time if there is bradycardia (below 100/min) or cyanosis.
- Types: central (no effort), obstructive (effort but no airflow) and mixed (commonest in prolonged spells).
- Apnoea of prematurity is a diagnosis of exclusion; it is commoner under 34 weeks or 1800 g and usually resolves by about 36 weeks post-conceptional age.
- Always look for a cause first: sepsis, hypoglycaemia, hypocalcaemia, hypothermia, anaemia, IVH, seizures, PDA, reflux.
- Treatment: gentle stimulation; bag-mask ventilation for prolonged spells; caffeine citrate (Akbar: 20 mg/kg load, then 5-10 mg/kg/day) or theophylline/aminophylline; nasal CPAP for mixed or obstructive apnoea; transfuse if anaemic.
Apnoea in a term baby is never apnoea of prematurity; it always has a cause such as asphyxia, seizures, IVH or sepsis.
Necrotising enterocolitis (NEC)
- Acquired inflammation and necrosis of the bowel, mainly in preterm babies after feeds are started.
- Causes: immature gut, ischaemia (asphyxia, polycythaemia, exchange transfusion, umbilical catheters), bacterial invasion, formula feeds and rapid increase of feeds.
- Features: feed intolerance with bile-stained aspirates, vomiting, abdominal distension and tenderness, blood in the stool; then lethargy, apnoea, temperature instability, shock, DIC.
- X-ray: dilated loops, thickened bowel wall, fixed loop; pneumatosis intestinalis (gas in the bowel wall) confirms it; portal venous gas; pneumoperitoneum if perforated.
- Treatment: stop feeds (nil by mouth, often 1-2 weeks) with TPN, nasogastric drainage, IV fluids, broad-spectrum antibiotics (with anaerobic cover), correction of shock and DIC; surgery for perforation or deterioration.
- Mortality about 30% in Akbar. Breast milk and slow feed advancement protect; probiotics may help.
Breast milk is the most important protective factor against NEC.
Intraventricular haemorrhage (IVH)
- Bleeding from the fragile, highly vascular germinal matrix (between the caudate nucleus and thalamus) into the ventricles.
- Mainly babies under 1500 g and under 34 weeks; Akbar gives an incidence of about 20% in babies under 1500 g.
- Occurs in the first 3-4 days; about half within 24 hours. Risk factors: extreme prematurity, asphyxia, RDS, ventilation, pneumothorax, swings in blood pressure, rapid volume or bicarbonate infusions.
- Often silent; or apnoea, bradycardia, fall in haematocrit, seizures, bulging fontanelle, coma.
- Cranial ultrasound diagnoses and grades it (I germinal matrix only; II in ventricle without dilatation; III with ventricular dilatation; IV with parenchymal bleeding).
- Complications: post-haemorrhagic hydrocephalus, cerebral palsy, epilepsy. Antenatal steroids reduce the risk.
Cranial ultrasound through the anterior fontanelle is the test of choice for IVH in preterm babies.
Other complications in brief
- Retinopathy of prematurity: screen at-risk babies; avoid excess oxygen.
- Bronchopulmonary dysplasia: oxygen need at 28 days after ventilation and oxygen for RDS.
- PDA: wide pulse pressure, continuous or systolic murmur, heart failure.
Care of the preterm baby
- Delivery in a unit with neonatal care; a paediatrician should attend; antenatal steroids to the mother.
- Resuscitation and temperature: plastic bag and cap, radiant warmer or incubator, kangaroo mother care once stable.
- Breathing: delivery-room CPAP for respiratory distress, surfactant for RDS, careful oxygen with saturation monitoring.
- Fluids: more than term babies (Akbar: about 60-80 mL/kg/day on day 1, rising daily to 150-180 mL/kg/day); daily weights.
- Feeding: breast milk is the best food. Babies under 34 weeks cannot coordinate suck and swallow and need tube feeds; very small or sick babies need parenteral nutrition. Start small volumes and advance slowly.
- Supplements: vitamin K 1 mg at birth; multivitamins; vitamin D; iron (2 mg/kg/day) from about 6-8 weeks; vitamin E for very small babies.
- Infection control: hand washing, asepsis, minimal handling.
- Monitoring: temperature, heart and respiratory rate, saturation, glucose, bilirubin, weight; screening for ROP, IVH and hearing.
Discharge when the baby is feeding by breast or bottle, gaining weight (10-30 g/day), keeping warm in an open cot, and has had no recent apnoea or bradycardia.
Small for gestational age and IUGR
Causes
| Group | Causes |
|---|---|
| Maternal | Hypertension and pre-eclampsia, chronic renal disease, long-standing diabetes with vascular disease, heart disease, malnutrition, poor weight gain, young age, smoking, alcohol, drugs, multiple pregnancy, poverty |
| Placental | Placental insufficiency, infarcts, abruption, small placenta, twin-to-twin transfusion |
| Fetal | Chromosomal disorders (trisomies 13, 18 and 21, Turner syndrome), congenital infections (TORCH), major malformations |
Symmetrical versus asymmetrical growth restriction
| Feature | Asymmetrical | Symmetrical |
|---|---|---|
| Measures | Weight low; head and length spared | Weight, length and head all small |
| Timing | Late pregnancy | Early pregnancy |
| Usual cause | Placental insufficiency, pre-eclampsia, maternal malnutrition, multiple pregnancy | Congenital infection, chromosomal disorders, maternal drugs |
| Look | Wasted (thin thighs, loose skin), alert, hungry | Proportionately small |
| Catch-up growth | Usually good | Often poor |
In asymmetrical IUGR the body "spares the brain": blood goes to the head first when the placenta fails.
Problems of SGA babies
- Hypoglycaemia: low glycogen stores, relatively large brain.
- Hypothermia: little subcutaneous fat.
- Perinatal asphyxia and meconium aspiration (placental insufficiency).
- Polycythaemia (chronic hypoxia drives red cell production), with hyperviscosity, jaundice and hypoglycaemia.
- Hypocalcaemia, neutropenia and thrombocytopenia.
- Infection; congenital anomalies in a minority.
- Later life: higher risk of hypertension, heart disease and type 2 diabetes.
Preterm versus SGA: who gets what
| Commoner in preterm babies | Commoner in term SGA babies |
|---|---|
| RDS, apnoea, IVH, NEC, PDA, ROP, jaundice and kernicterus, anaemia | Meconium aspiration, polycythaemia, asphyxia, hypoglycaemia |
Both share hypothermia, hypoglycaemia, hypocalcaemia, infection and feeding problems.
Management of SGA babies
- Planned delivery with a paediatrician present.
- Early feeding (within the first hour, then every 2-3 hours) and frequent glucose checks.
- Thermoneutral care; check haematocrit for polycythaemia.
- Look for congenital infection, malformations and chromosomal disorders.
Large for gestational age
Causes: large parents (constitutional), infant of diabetic mother, Beckwith-Wiedemann syndrome, some post-term babies, hydrops (Rh disease), transposition of the great arteries.
Problems: birth trauma (shoulder dystocia, fractured clavicle, Erb palsy), asphyxia, hypoglycaemia (from hyperinsulinism in IDM, Rh disease and Beckwith-Wiedemann), polycythaemia.
Care: early feeds and glucose monitoring; examine for birth injuries.
Post-term babies
- Born after 42 weeks. Usually no cause found; sometimes anencephaly or trisomy 18.
- Look: no lanugo, little vernix, long nails, abundant hair, dry, peeling, wrinkled skin, alert; meconium staining if the placenta failed.
- Problems: meconium aspiration, asphyxia, hypoglycaemia, polycythaemia.
Expect: definitions of preterm (before 37 weeks), LBW (below 2500 g), VLBW, ELBW, SGA (below 10th centile) and LGA (above 90th centile); a term baby of 2 kg being SGA but not preterm; symmetrical versus asymmetrical IUGR with their causes and catch-up growth; Ballard score; rapid visual signs of maturity; problems of prematurity versus SGA (RDS and IVH in preterm, meconium aspiration and polycythaemia in SGA); apnoea of prematurity with caffeine; NEC with pneumatosis intestinalis and breast milk protection; IVH from the germinal matrix diagnosed by ultrasound; tube feeding under 34 weeks; birth trauma and hypoglycaemia in LGA babies.
Quick revision
- Preterm under 37 weeks; LBW under 2500 g; VLBW under 1500 g; ELBW under 1000 g.
- SGA under 10th centile; LGA over 90th centile.
- Asymmetrical IUGR: head spared, placental, good catch-up. Symmetrical: all small, infection or chromosomal, poor catch-up.
- Preterm problems: hypothermia, hypoglycaemia, RDS, apnoea, IVH, NEC, PDA, jaundice, infection, ROP, BPD.
- SGA problems: hypoglycaemia, polycythaemia, asphyxia, meconium aspiration.
- Ballard score accurate to 2 weeks; best at 30-42 hours.
- Apnoea of prematurity: under 34 weeks, resolves by 36 weeks; caffeine citrate.
- NEC: bloody stools, distension, pneumatosis; stop feeds, antibiotics, surgery if perforated.
- IVH: germinal matrix, first 72 hours, cranial ultrasound.
- LGA: IDM, Beckwith-Wiedemann; birth trauma and hypoglycaemia.
Written by The House Job from standard references (Basis of Paediatrics by Pervez Akbar; Nelson Essentials of Paediatrics).
FAQ
Is every low birth weight baby preterm?
No; a term baby can be low birth weight because of growth restriction, and that baby is SGA rather than preterm.
Which type of growth restriction has the better outlook?
Asymmetrical growth restriction, where the head is spared, usually shows catch-up growth; symmetrical restriction often does not.
Why do preterm babies under 34 weeks need tube feeding?
They cannot yet coordinate sucking, swallowing and breathing, so oral feeds risk aspiration.
What is the first drug for apnoea of prematurity?
Caffeine citrate, after sepsis and other causes have been excluded.