37 weeks pregnant and burnt a plastic cup in microwave. when i opened microwave, fumes poured out. i inhaled much of the fumes. any risk to my baby?

Not if you are okay: At this point in pregnancy there is little risk unless you damaged your lungs or were sickened by inhaling the fumes. It shows what a good mom you are going to be that your first concern was for the baby. Best wishes.

Plastic Fumes: inwould assume you quickly aired out you house and were not overly exposed. If you are not short of breath and having no respiratory symptoms I doubt very strongly that there will be any short or long term effects to your baby. Hoping you have an eventful pregnancy.

No significant risk: Plastic fumes are not good for anyone but by 37 weeks your baby is almost fully developed and this should not have a significant effect. This would have been more worrisome in the first trimester (but even then would probably be OK unless you really inhaled a large amount). Don't worry. Hope your delivery goes smoothly!