Final answer:
The likely diagnosis for the patient is a missed miscarriage.
Step-by-step explanation:
The likely diagnosis for a patient presenting with vaginal bleeding, an LMP period that occurred 16 weeks ago, a fundal height of 20 cm, and a beta-hCG of 85,000mIU/mL is a missed miscarriage. In a missed miscarriage, the embryo or fetus has stopped developing, but the pregnancy tissue remains in the uterus. The vaginal bleeding is a result of the body expelling the non-viable pregnancy. It is important for the patient to follow up with their healthcare provider for further evaluation and management.