Thanks for your query.
Rubella is a viral infection known as german measles
also. If it occurs in early pregnancy
transmitted to the fetus and cause fetal congenital rubella
syndrome (heart deformity
, fetal deafness
and mental retardation).
It can be diagnosed by a TORCH test (every pregnant women go for a rubella test for IgM, IgG).
In your case the IgM test is positive for rubella, so you should not continue your pregnancy and go for termination as your doctor says.