What effects can rhesus disease have on my baby?

RhoGam can obviate. Rhogam is an injectible medication that can remove (obviate) any future problems with the rh negative issue. There is a great pamphlet for more on the subject here: http://www.Acog.Org/publications/patient_education/bp027.Cfm.
Hydrops Fetalis. ...Is an accumulation of fluid in at least two of the fetal body compartments. It can lead to congestive heart failure, kidney failure etc. In the fetus. Prior to the 1970s the most common cause was maternal antibodies against the rhesus factor on the fetus' blood cells, which were then coated with antibodies and destroyed (rhesus disease). A medicine called Rhogam has made this rare now.
Rhesus factor. I suppose you mean the rhesus factor of the blood typing system.When rh positive blood is given to a factor negative person, the body makes antibodies that will reject & destroy future rh+ blood. An rh- mother today is usually given a shot during pregnancy that prevents her body from developing antibodies.If present, the antibodies could break down babies blood & cause damage or death.