Large for Gestational Age

Babies are defined as being large for gestational age (also known as macrosomia) when the weight of the newborn is more than 4.5kg at birth. During pregnancy, an estimated fetal weight above the 90th centile is considered large for gestational age.


Causes of Macrosomia

  • Constitutional
  • Maternal diabetes
  • Previous macrosomia
  • Maternal obesity or rapid weight gain
  • Overdue
  • Male baby



The risks to the mother include:

  • Shoulder dystocia
  • Failure to progress
  • Perineal tears
  • Instrumental delivery or caesarean
  • Postpartum haemorrhage
  • Uterine rupture (rare)


The risks to the baby include:

  • Birth injury (Erbs palsy, clavicular fracture, fetal distress and hypoxia)
  • Neonatal hypoglycaemia
  • Obesity in childhood and later life
  • Type 2 diabetes in adulthood


TOM TIP: If you only remember two things about macrosomia, remember that it is caused by gestational diabetes, and there is a significant risk of shoulder dystocia during birth. 



Investigations for a large for gestational age baby are:

  • Ultrasound to exclude polyhydramnios and estimate the fetal weight
  • Oral glucose tolerance test for gestational diabetes


Most women with large for gestational age pregnancy will have a successful vaginal delivery. NICE guidelines (2008) advise against induction of labour only on the grounds of macrosomia.

The main risk with a large for gestational age baby is shoulder dystocia. The risks at delivery can be reduced by:

  • Delivery on a consultant lead unit
  • Delivery by an experienced midwife or obstetrician
  • Access to an obstetrician and theatre if required
  • Active management of the third stage (delivery of the placenta)
  • Early decision for caesarean section if required
  • Paediatrician attending the birth


Last updated September 2020
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