Derivation
If the woman states her period has not returned since the birth in question, then if the woman is pregnant, M7 is calculated as the difference between the date of interview and the child in question'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 the child's date of birth. If the woman's period has returned since the child's birth, then the literal question is asked. It is further adjusted based on the flag condition of M28.