If I were you and not on birth control pills I would not have intercourse when swinging unless I felt 99% certain that I was not ovulating, plus, I'd
always use a condom no matter what time of the month it was.
Getting pregnant by accident is nothing to take lightly, especially when it could be from a man other than your husband.
I feel there are lots of fun sexy things you can do with people when you are at a high risk of getting pregnant (during ovulation) besides intercourse.
Play safely. Play creatively.
LM