Final answer:
A fundal height of only 15 cm at 20 weeks pregnancy, along with a boggy and tender uterus, suggests a missed abortion rather than ectopic pregnancy, placental abruption, or uterine fibroids.
Step-by-step explanation:
When encountering a pregnancy at 20 weeks with a fundal measurement of only 15 cm that feels boggy and tender, the clinical suspicion should lean towards a missed abortion. A missed abortion is a pregnancy loss where the embryo or fetus has died but the uterine contents have not been expelled. The symptoms described do not commonly associate with ectopic pregnancy, as this condition usually presents earlier in the pregnancy with different clinical features. Placental abruption typically presents with painful bleeding and a firm, tender uterus. Uterine fibroids, on the other hand, could be a cause of an irregularly shaped and enlarged uterus, but are usually not tender unless degeneration occurs. Given the fundal height measurement and a boggy, tender uterus, a missed abortion seems most plausible, and further evaluation with ultrasound will be needed to confirm the diagnosis and manage the condition.