NEW YORK (Reuters Health) - Women who receive a vaccination against rubella 1 month before becoming pregnant should not worry that they have endangered the health of their fetus, according to experts.

Previously, doctors were told that women given a vaccine against rubella less than 3 months before becoming pregnant were at risk of becoming infected by rubella and passing it onto their children. This fear stems from the fact that the vaccine contains a so-called "live" form of the virus, which, in a few cases, can actually give the patient the disease.

Rubella--also known as German measles--has largely been eradicated in the US thanks to widespread use of the vaccine, first introduced in 1969. However, doctors still administer the rubella vaccine, primarily to ensure that pregnant women will not contract the infection. When a pregnant woman becomes infected with rubella, especially during the first trimester, she can pass the infection on to the fetus. This can cause a miscarriage, stillbirth or congenital rubella syndrome (CRS)--a collection of severe birth defects that includes mental retardation, heart disease, deafness and cataracts.

In many instances, the rubella vaccine is combined with the measles and mumps vaccines.

In October 2001, the US Centers for Disease Control and Prevention (CDC) shortened the interval between the rubella vaccine and pregnancy from 3 months to 1 month. Dr. Laura Riley of Massachusetts General Hospital in Boston told Reuters Health that this change came out of a number of cases in which women mistakenly became pregnant less than 3 months after receiving a rubella vaccine, and then gave birth to healthy babies.

"If you happen to get a vaccine, you only have to wait one month before trying to get pregnant," Riley said.

Now, in a statement released Friday by the American College of Obstetricians and Gynecologists (ACOG), a committee reaffirms the CDC's recommendations, shortening the safe window from vaccine to pregnancy from 3 months to 1 month. Riley, chair of ACOG's committee on obstetric practice, said she felt it was important to issue a separate recommendation, since many doctors may have missed the first CDC report.

"I don't think that (the CDC publication) is always read by certain subspecialties," she said.

Most women who grow up in the US are vaccinated against rubella during their childhood, but some who immigrate here from other countries may not have been. In addition, she noted, some parents opt out of vaccinating their children for various reasons, while some women may have been vaccinated before, but still did not become immune to the disease.

In cases where women are vulnerable to contracting rubella, they should not receive the vaccine if they are already pregnant, Riley said, and should instead wait until they have delivered the baby.

The researcher noted that all pregnant women are tested to see if they are vulnerable to rubella during their first prenatal exams, so they will know right away if their fetus is at risk of the disease. However, if they know they have not received the vaccine, and are thinking about becoming pregnant, the wisest thing is to schedule the vaccine and wait an additional month before trying to conceive, Riley said.

"Go ahead and figure out if you're rubella-immune" before getting pregnant, Riley said.