Warning: these figures indicate the number of cases found in the data file. They cannot be interpreted as summary statistics of the population of interest.
MIDX reports the young child's line number in the woman respondent's maternity history. For children who are included in the maternity history (pregnancy and postnatal care section of the questionnaire, normally children under age 3, 4, or 5), the value of MIDX is the same as the child's line number in the birth history (BIDX).
According to the DHS Recode Manuals, "For twins, the information in their entries will be identical for all variables relating to prenatal care."