When should a woman with a nonexistent rubella titer level receive the rubella vaccine during her pregnancy?

The rubella vaccine is a live attenuated vaccine that is contraindicated during pregnancy. If a woman is found to have a nonexistent rubella titer, indicating she is not immune to rubella, the appropriate timing for vaccination is after delivery. Administering the vaccine while pregnant poses a risk to the developing fetus, hence it should be avoided during all trimesters. Vaccination after delivery allows for the woman to develop immunity without putting the fetus at risk, ensuring both maternal health and the well-being of any future pregnancies.

In contrast, vaccination during any trimester of pregnancy would be inappropriate due to the potential risks associated with live vaccines during this critical time. Therefore, the correct practice is to wait until after delivery to administer the rubella vaccine.