Measles (also known as Rubeola) is a viral disease that usually produces fever, cough, conjunctivitis ("pink eye," but not quite the same as the "pink eye" seen with colds and earaches), a red, bumpy rash, and a rash ("Koplik's spots") inside the cheeks. It can be complicated by secondary ear infections, diarrhea, croup, and mild pneumonia. Most children are now vaccinated against measles with the MMR (Mumps-Measles-Rubella) vaccine.
Before the vaccine came along, measles epidemics occurred about every two years, usually in winter and early spring when nonimmune children were together in school, and most measles patients were preschoolers and young elementary-school kids. Nowadays, most cases are seen in unvaccinated children (kids younger than 15 months who haven't had the vaccine yet, and preschool kids who should have had the vaccine but haven't) and older children -- some in college -- who received one dose of vaccine but did not become immune.
Most pregnant women are immune by the trime they become pregnant and cannot get the measles because they either have had the measles or they were vaccinated.
Vaccination against measles is not recommended during pregnancy because the vaccine contains live virus. Risks to the pregnancy are the fetus are low if a pregnant woman is vaccinated by mistake, and termination of pregnancy is not recommended for that reason.
Contrary to the Rubeola (measles) virus, which is unlikely to harm the fetus, the German measles (rubella) virus is different and can have a negative effect on the fetus.