Very important and I would like to know too. Presently we calculate the weight gain over one week span. Use the weight difference divided by the first weight to obtain g/kg/d and use 10-15 g/kg/d as a adequate weight gain. This is what we use. Eager to hear from the experts.

we also calculate the weight gain over one week span ,use the difference divided by the first weight to get g/kg/day .I think you can use different span as long as you make it the standard in your unit ,the good thing about the one week span is that it is an enough time to judge on the growth and its not a long time to make a delay in   intervention in neonates who are not gaining weight .will love to hear what others do too!

We  calculate that newborn increases about 1 gram per hour, during the first month, after the first week of life when initially lost weight (10%); this is useful when balances are made every 8 to 12 hours or if you prefer the weight gain is about 20 g per day.

We also calculate the weight gain in one week, by taking the difference in one week divided by the weight in the last day. We accept as adequate a weight gain of 15 to 20 mg/kg/d.

Although the value obtained using linear vs exponential models will not differ significantly over short time periods, another method is to use the exponential growth model described by Patel et al. GV = [1000 x ln(Wn/W1)]/(Dn-D1).

Reference: Patel AL, Engstrom JL, Meier PP, Kimura RE. Accuracy of methods for calculating postnatal growth velocity for extremely low birth weight infants. Pediatrics 2005;116(6):1466-1473.

We use 10-20 grams/kg/ day for weight.

1-1.5cm head circumference per month for first year of life, and about 1-2 cm lenght  per month in first year of life. These are derived from various charts including the famous Lubchenco charts. Preterm infants