During which trimester is the MMR vaccine contraindicated?

The MMR (Measles, Mumps, and Rubella) vaccine contains live attenuated viruses, which can pose a risk during pregnancy, particularly in the first trimester. The primary concern is the potential for the vaccine to cause harm to the developing fetus. While some guidelines do suggest that the MMR vaccine is generally avoided in all trimesters of pregnancy, the first trimester is specifically highlighted due to the critical development stages the fetus undergoes during this time.

In the third trimester, although the focus tends to be on ensuring the health and safety of both the mother and fetus, the risk associated with live vaccines is largely about their use during pregnancy overall, especially before conception or early on. In the postpartum period, the vaccine can be administered safely, as there is no risk to a non-pregnant individual. Therefore, the contraindication to receiving the MMR vaccine is strictly noted during pregnancy, focusing particularly on the first trimester, which can also extend the recommendation to avoid it throughout pregnancy to be extra cautious.