My wife, 36, is pregnant of 8 months. She is having swelling on her legs and feet. Anything serious? We have 11 year old daughter.

Blood pressure. Swelling of the extremities is almost universal problem late in pregnancy. It is important though that she have her blood pressure checked by a doctor. Sometimes the swelling to indicate a blood pressure problem called preeclampsia. Usually the swelling is just swelling.
This could be . Related to pregnancy. Let her see her oby and get checked for leg clot, heart or kidney problems. Take care!
Congratulations. Fluid retention may be a normal side effect of decreased return blood flow from the lower extremities--especially if on her feet a lot. She should see her ob/gyn for evaluation anyway. Good luck!