How to investigate the infant with inadequate weight gain

Average weight gains in the first year of life

The Royal Women's Children's Hospital (Melbourne, Australia) clinical guidelines for history taking, assessment, investigations, and management of poor infant weight gain are found here. The summaries below are taken from that document.

Here is a very rough guide to average weight gains in the first year of life, which are useful to have in mind if you're a health professional.

Age (months)	Average gain (grams/week)
0-3	150–200
3-6	100-150
6-12	70-90

Investigation of infant with inadequate weight gain

Here are the RWCH clinical guidelines for investigation of the infant with inadequate weight gain.

All ages

Urine: Urinalysis, microscopy and culture (especially infants < 12 months of age, as occult urinary tract infection can present with slow weight gain)

Blood:

• FBE, ferritin, UEC, TSH, glucose, LFT

• If on solids or feeds containing gluten - coeliac serology and total IgA

• Micronutrients – especially active B12 if suspicion of malabsorption or restricted dietary intake

Stool: Microscopy, fat globules, fatty acid crystals

Children older than 12 months

Add in ESR, faecal calprotectin

Specific investigations for underlying metabolic, immune or genetic cause should be performed in consultation with specialist services