If a pregnant woman is not immune to the rubella virus and becomes infected in the first half of her pregnancy (before 20 weeks), the virus is capable of causing abnormalities in her baby. For women who become infected in the first 8 to 10 weeks of their pregnancy (measured from the first day of the last menstrual period) their baby has about a 90% chance of developing abnormalities. If a woman becomes infected between 10 and 16 weeks of the pregnancy, the risk to her baby decreases to about 10 to 20%. Effects on the baby from 16 to 20 weeks of the pregnancy are very rare and rubella infections experienced after 20 weeks should not affect the baby.
If the woman has had immunity to rubella in the past, but her immunity has diminished over time, and she then experiences a rubella infection during early pregnancy, the chances of her baby being affected are very small, no matter what stage of the pregnancy she is at.
NOTE: Be aware that there is a big difference between a pregnant woman experiencing the standard measles infection and the rubella virus (or German measles). While the standard measles infection usually makes the person feel more unwell, and the signs can last longer (when compared to the rubella virus), the effects of the standard measles infection during pregnancy are the possibility of miscarriage, or premature labour. Standard measles does not cause abnormalities in unborn babies, unlike the rubella virus, which can cause abnormalities of the baby (but not necessarily lead to miscarriage or premature birth). The type of measles you have can only be determined by a blood test.
An unborn baby of less than 8 weeks
gestation can experience a combination of multiple abnormalities if exposed to the rubella virus. The effects normally relate to the developmental stage the baby is at during the time of the infection and can include: