Marino's mom is Caitlyn's first wife, Chrystie Crownover, who she was married to from 1972 to 1981.
According to a source, Marino is expecting a boy this October, reported Us magazine.
The 35-year-old is already mom of daughters Isabella and Francesca with husband Mark.
During her sit-down interview with Diane Sawyer post her gender transition, Jenner, 66, admitted she was absent from Marino's and sons Burt, Brandon and Brody's lives.
"The big, formative years for them, I was really struggling with these issues," Jenner had told Sawyer.
The clan has, however, since repaired their relationship.