What condition is indicated by uterine bleeding at 18 weeks' gestation with no products expelled and an open cervical os?

The scenario described, where there is uterine bleeding at 18 weeks' gestation, an open cervical os, and no products of conception expelled, is indicative of an inevitable abortion. In this case, the open cervical os suggests that the cervix is already dilating, which indicates that a miscarriage is likely to occur.

In inevitable abortion, the process of expulsion of the pregnancy is underway, but the products have not yet passed. The presence of active bleeding and the cervical changes signify that the pregnancy cannot be maintained, leading to the conclusion that fetal loss is imminent.

This contrasts with other conditions such as threatened abortion, where there may be bleeding but the cervical os remains closed, indicating that the threat of miscarriage exists but has not yet resulted in progression. Similarly, incomplete abortion occurs when some products of conception have been expelled while others remain, and missed abortion refers to a situation in which the fetus has died but has not been expelled and may not be accompanied by bleeding or cervical change.

Thus, the conditions that are present distinctly point towards an inevitable abortion, characterized by the combination of bleeding, an open cervical os, and the absence of expelled products.