DOB1STKIDCMC (V211) reports the century month code (CMC) for the date of the woman's first birth.
The Guide to DHS Statistics (2003) explains the use and calculation of CMC values as follows:
Century month codes (CMC) are particularly important to check consistency of dates, to calculate intervals between events, and to impute dates when the information for an event is missing or partially complete.
Century month codes (CMC) are calculated by multiplying by 12 the difference between the year of an event and 1900. That year was chosen as the reference period because all of the DHS relevant events occurred during the twentieth or twenty-first centuries. The month of the event is added to the previous result.
CMC = (Year - 1900) * 12 + Month
For example, the CMC for June 2002 will be:
CMC = (2002 - 1900) * 12 + 6 = 1230
In other words, 1,230 months have elapsed since January 1900 to June 2002. Based on CMC it is possible to calculate the month and year using the following formulas:
Year = int( ( CMC - 1 )/12 ) + 1900
[int(x) is the integer part of x]
Month = CMC - ( ( Year - 1900 ) * 12 )