I left school in 1980 and got a job as a trainee accountant, taking firstly A levels and then professional exams, and ultimately qualifying in 1988. I worked at 3 different places over those 8 years, and in all three, there were women at all levels, from trainee through to seniors/managers and partners. Yes, the women in qualified/senior roles were a minority, but they were there.
In the 90's it was more evenly matched between men and women, and in the noughties, I started to see firms with a majority of women in manager/partner level roles.
Obviously, I don't know what it was like in the 70s as I was still at school, but the fact that there were manager/partner level women at firms I worked at in the 80s suggests that there were women trainees in the 70s as you're typically looking at 10+ years to get to partner level!
As for pregnancy, there was no thought in the 80s that pregnant women wouldn't be returning to the workplace after their maternity leave. I can't remember anyone not returning. A few came back part time, but pretty sure they all came back.