BIRTHWT (M19) is a 4-digit numeric variable with 3 implied decimal places.
9995 = 9995+
9996 = Not weighed at birth
9997 = Don't know
9998 = Missing
9999 = NIU (not in universe)
For children born in the three to five years before the survey, BIRTHWT (M19) reports the child's birthweight in kilos with three implied decimal places (or, alternatively stated, in grams with no decimal places). Children who were not weighed are coded 9996.
Apart from universe differences and slight differences in question wording, BIRTHWT (M19) has no comparability problems.
The measure of weight used to collect the information for BIRTHWT depends on the system of measurement in place in the country. Some countries collected birthweight in grams (a total of four digits); others used kilograms defined to one decimal place (two meaningful digits, followed by two zeros); still others used pounds and/or ounces. These original measurements are stored in country-specific variables, while BIRTHWT contains the weight consistently converted to kilograms.
Comparability - Standard DHS
BIRTHWT (M19) is included in the standard DHS questionnaire for Phase 2 forward.