mother-to-be

noun2

1. •
   A pregnant woman, especially one expecting her first child.

   • The ideal position for a back massage for the mother-to-be is to sit astride a chair supported by cushions. — 2000
2. •
   A woman whose partner is pregnant.

   • I don't know how other lesbian, nonbiological mothers-to-be, who tried to get pregnant and could not, might experience their partners' pregnancy. — 2010