What kind of outdoor activities should I avoid while pregnant?

Injury prevention. Avoid anything wigh a high risk of falls or accidents such as biking, jet skiing, four wheel driving, and tackle football.
I agree with.... Dr. Dimino. The main concern is an injury that could either compromise your child or the structures supporting your child's development. For injury prevention, i advise folks to not engage in any activity that's more than "self-propelled". In other words, if gravity could act upon you or if a machine can propel you but doesnt enclose you, i would avoid the activity. Let common sense be your guide.