If you are a STATA user, there is a new package called "haz06" which you can install that will calculate the WHO standards using the height and age variables, which is particularly convenient when you are using older DHS surveys that only have the old standards. You have to be careful that you are using age and height in the right units (months and cm - I think).

gen hw2_2 = hw2/10           /// Convert weight in Kg
gen hw3_2 = hw3/10           /// Convert height in cm

zscore06, a(hw1) s(b4) h(hw3_2) w(hw2_2)

gen HAZ = haz06 * 100

list HAZ hw70