Okay, let's tackle this question. The patient is a 26-year-old G1P0 with moderate vaginal bleeding but no pain or contractions. The physical exam shows a closed cervix and no cramping. So, first, I need to consider the possible causes of vaginal bleeding in the first trimester.

The options aren't given, but the correct answer is likely something like "threatened abortion" or "placental abruption," but since there's no pain or contractions, maybe threatened abortion is more likely. Wait, but the question mentions it's in the OG department—obstetrics. Let me think again.

Threatened abortion typically presents with vaginal bleeding in early pregnancy without cervical dilation or contractions. The cervix is closed here, which fits. Placental abruption usually comes with pain and uterine tenderness, which she doesn't have. Ectopic pregnancy can cause bleeding, but the cervix is closed and there's no pain, which might make that less likely unless there's a corpus luteum bleed. Placenta previa can cause painless bleeding, but that's usually in the second or third trimester. Since she's G1P0, maybe it's a threatened abortion.

Wait, but the question says "moderate" bleeding. Threatened abortion is possible. If there's no cramping or contractions, and cervix is closed, then it's a threatened abortion. If the cervix were open, it would be inevitable abortion. So the key points here are the absence of pain, contractions, and a closed cervix.

Other options could include incomplete abortion, but that usually has an open cervix. Placenta previa is later. Ectopic would have other signs like adnexal tenderness, maybe not. So the correct answer is probably threatened abortion. Let me make sure. The clinical pearl here is that threatened abortion is diagnosed when there's vaginal bleeding in early pregnancy without cervical dilation or contractions. The student should remember the key features: bleeding, no pain, closed cervix. The options not correct would be other causes with different presentations.

**Core Concept**
This question examines the differential diagnosis of first-trimester vaginal bleeding, focusing on distinguishing between **threatened abortion**, **inevitable abortion**, **placenta previa**, and **ectopic pregnancy**. Key clinical features include absence of pain, closed cervix, and no contractions.

**Why the Correct Answer is Right**
Threatened abortion is characterized by **vaginal bleeding in early pregnancy without cervical dilation or uterine contractions**. The patient’s closed cervix, lack of pain or cramping, and absence of contractions align with this diagnosis. Bleeding may result from implantation-related vascular disruption or subchorionic hematoma. The speculum finding of a clot at the vault further supports localized bleeding without active expulsion.

**Why Each Wrong Option is Incorrect**
**Option A:** *Placenta previa* presents with **painless, bright red bleeding** in the second/third trimester, not the first.
**Option B:** *Ectopic pregnancy* typically causes **acute lower abdominal pain** and adnexal tenderness, absent here.
**Option C:** *Inevitable abortion* requires **cervical dilation** or effacement, which

✓ Correct Answer: A. Threatened abortion