Understanding Society User Support

Dear UKHLS team,

The variables on the newborn dataset have a large amount of missing data coded as 'inapplicable' (see two examples from wave 5 at the bottom). I've looked into the skip patterns but can't understand why the large numbers. Could you please let me know?

Many thanks!
Laia

birthweight  |      Freq.     Percent        Cum.
-------------------------+-----------------------------------
                 missing |          1        0.08        0.08
            inapplicable |        569       42.94       43.02
              don't know |          5        0.38       43.40
answer in lbs and ounces |        662       49.96       93.36
     answer in kilograms |         88        6.64      100.00
-------------------------+-----------------------------------
                   Total |      1,325      100.00

child's sex | Freq. Percent Cum.
-------------+-----------------------------------
inapplicable | 1,283 96.83 96.83
don't know | 1 0.08 96.91
boy | 18 1.36 98.26
girl | 23 1.74 100.00
-------------+-----------------------------------
Total | 1,325 100.