Derivation
If the woman states her period has not returned since her last birth, then if the woman is pregnant, M7 is calculated as the difference between the date of interview and her last child's date of birth, adjusting for the number of months she has been pregnant (V008 - V214 - B3); if the woman is not pregnant, then it is simply the difference between the date of interview and her last child's date of birth. If the woman's period has returned since her last birth, then the literal question is asked. It is further adjusted based on the flag condition of M27.