Is it possible to miscarry in the 3rd trimester?

No. Sort of, but it wouldn't be called a miscarriage. If a fetus were to die in third trimester it would be an intrauterine fetal demise. If it were to deliver alive it would be preterm labor. Miscarriage technically refers to delivery of a fetus prior to 20 weeks.
???????????????????? If you get to the 3rd trimester and you deliver a live baby that is called premature delivery or hopefully would not happen- if the baby is born not alive- that is called as stillbirth.

Related Questions

What happens if you've miscarried in the 2nd or 3rd trimester, what was the reasoning?

Many causes. Infections, fetal anomalies (chromosomal ), weak cervical structure, trauma, drugs are common causes behind miscarriages in 2nd trimester. It may be due to chromosomal issues. See you OB-GYN to get further information. Regards Dr M. Read more...