i hear this all the time in the sub and it's usually when they bring up the scene where Marsha tells Nate that Maddy would baby trap him, but when did Marsha baby trap Cal?

Cal kisses Derek and then the following morning Marsha calls him and tells him that shes pregnant with Aaron. This isn't surprising as they we're having a lot of sex. He cries but ultimately he stays and helps her raise the baby. I would assume because of Cals dad and the era, they married before having Aaron, Cal didn't go to college but got a job instead. After Aaron it was Nate and then the 3rd Son.

So how did Marsha baby trap Cal? especially when Marsha didn't know Cal was gay until much later.