Okay, let's tackle this question about blighted ovum. The user provided the question but didn't list the options. Hmm, that's a bit tricky. But since the correct answer is given as an empty option, maybe the options were missing in the original input. Wait, the user mentioned that the correct answer is right, so I need to figure out the correct answer first.

Blighted ovum, also known as anembryonic pregnancy, is when a gestational sac develops but there's no embryo. The key features would include a gestational sac with no embryo, and often the sac might be larger than expected for the gestational age. The yolk sac might be present, but the embryo doesn't develop. The options might have included things like absence of a yolk sac, presence of a normal embryo, or other features.

The correct answer would likely be something like "A gestational sac without an embryo." The other options might be incorrect because they could mention a normal embryo, presence of fetal heart activity, or other signs of a viable pregnancy. For example, an incomplete abortion would have some products of conception but not an empty sac. Ectopic pregnancy is a different condition altogether. Hydatidiform mole involves abnormal placental tissue, not an empty sac.

So, the core concept here is understanding the definition and distinguishing features of a blighted ovum. The clinical pearl is to remember that ultrasound is key in diagnosis, showing a sac without an embryo. The correct answer should be the option that states the absence of an embryo within the gestational sac.

**Core Concept**
Blighted ovum (anembryonic pregnancy) is a type of early pregnancy loss where a gestational sac forms but no embryo develops. It is diagnosed via **transvaginal ultrasound** showing an empty sac with or without a yolk sac, and absent embryonic/fetal pole. This differs from other pregnancy complications like ectopic pregnancy or molar pregnancy.

**Why the Correct Answer is Right**
The hallmark of a blighted ovum is a **gestational sac without an embryo**. The sac may grow to a size consistent with early pregnancy, but no fetal pole or cardiac activity is present. This occurs due to **chromosomal abnormalities** in the embryo, leading to arrested development. Diagnosis is confirmed by ultrasound, and management typically involves expectant, medical, or surgical intervention.

**Why Each Wrong Option is Incorrect**
**Option A:** If this stated "Presence of a viable embryo," it is incorrect because a blighted ovum lacks embryonic development.
**Option B:** If this described "Fetal cardiac activity," it is incorrect as cardiac activity is absent in blighted ovum.
**Option C:** If this mentioned "Products of conception with intact embryo," it refers to an incomplete abortion, not a blighted ovum.
**Option D:** If this described "Villous edema and trophoblastic hyperplasia," it refers to hydatidiform mole, not anembryonic pregnancy.

**Clinical Pearl / High-Yield Fact**
Remember the **"empty sac"** on ultrasound as the key diagnostic feature. Differentiate from **ectopic pregnancy** (sac outside uterus), **missed abortion** (non-viable but with embryonic remnants), and **hydatidiform mole** (abnormal placental tissue

✓ Correct Answer: A. Avascular villi