The Collaborative International Dictionary of English v.0.48:

Lying-in \Ly"ing-in"\, n.
   1. The state attending, and consequent to, childbirth;
      confinement; as, a lying-in hospital.
      [1913 Webster]

   2. The act of bearing a child.
      [1913 Webster]

WordNet (r) 3.0 (2006):

lying-in
    n 1: concluding state of pregnancy; from the onset of
         contractions to the birth of a child; "she was in labor for
         six hours" [syn: parturiency, labor, labour,
         confinement, lying-in, travail, childbed]