The runway star is due to give birth to a boy - a little brother for her 11-month-old son Zander - on 23 March (13).
Rizer tells People.com, "(Husband) Alex (Mehran) and I always wanted a big family. We want to have as many kids as we can - within reason."
However, the expectant mum admits she isn't enjoying the pregnancy process and can't wait to get it all over with: "I'm not that girl that's like, 'I love it, I can embrace it.' I'm like, 'When is it going to end?'"
Rizer and businessman Mehran wed in 2010.