Section W21 (REC21) Reproduction
The birth history contains up to 20 entries for births, and is ordered in reverse order such that the last birth is
given first in the birth history and the first birth is given last. For respondents with more than 20 births, the
birth history contains the last 19 births plus the first birth. However, all variables relating to intervals between
births are calculated based on the actual births, and not just the births given in the birth history. The variable
V224 contains the count of entries in the birth history, and is thus the index to the last entry in the birth
history which contains the information relating to the first birth.

BIDX Birth history index numbers the entries in the birth history from 1 to n, where the nth birth is
the first birth.
BORD Birth order number gives the order in which the children were born and so is the reverse
order from BIDX.

MIDX Index to the birth history. All births in the last three/five years have entries in this section,
and thus the index increases by one each entry. See the example maternity history below.
For twins the information in their entries will be identical for all variables relating to prenatal
care.