Large for gestational age

Question 1

What is large for gestational age?

Answer 1

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.

Question 2

Causes of macrosomia?

Answer 2

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

Question 3

Macrosomia risks to mother?

Baby?

Answer 3

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.

Question 4

Investigations for large for gestational age?

Answer 4

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

Question 5

Management for large for gestational age?

Answer 5

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