<prompt> Decidual space is obliterated by:10 th week12 th week18 that week16 th week  <response>: Decidual space is the space between decidua capsularis and parietalis seen in early pregnancy because the gestational sac does not fill the uterine cavity. By 14-16 weeks the gestational sacred has enlarged to fill the uterine cavity completely by 4 th month 16 weeks. Ref: Datta Observe 9e pg 22. 