Frequencies for first 10,000 rows of gestfl variable in namcs2012 dataset :

 Was week of gestation |
    calculated by NCHS |
           during data |
           processing? |      Freq.     Percent        Cum.
-----------------------+-----------------------------------
    Calculated by NCHS |          6        0.06        0.06
Not calculated by NCHS |      9,994       99.94      100.00
-----------------------+-----------------------------------
                 Total |     10,000      100.00

by Jean Roth , jroth@nber.org , 28 Mar 2016