**Question:** Ectopic pregnancy can be ruled out on ultrasound by:

A. Identification of an intrauterine gestational sac
B. Absence of a gestational sac
C. Presence of a dilated uterine cavity
D. Absence of a fetal heartbeat

**Core Concept:** Ectopic pregnancy is a type of pregnancy where the fertilized ovum implants itself in a location outside the uterine cavity. The key ultrasound findings in ruling out ectopic pregnancy include intrauterine gestational sac, dilated uterine cavity, and fetal heartbeat.

**Why the Correct Answer is Right:** Ectopic pregnancy can be ruled out when ultrasound shows an intrauterine gestational sac, indicating that the pregnancy is inside the uterus. This is because, in an ectopic pregnancy, there would not be a gestational sac inside the uterus.

**Why Each Wrong Option is Incorrect:**

A. Identification of an intrauterine gestational sac is important to confirm the presence of a pregnancy within the uterus. However, it is not sufficient for ruling out ectopic pregnancy since an intrauterine gestational sac can still be present in an ectopic pregnancy.

B. Absence of a gestational sac is not sufficient to rule out ectopic pregnancy either, as it could be due to early gestation or a missed intrauterine pregnancy.

C. A dilated uterine cavity may indicate a ruptured ectopic pregnancy or a very advanced ectopic pregnancy, but it is not specific enough to rule out all ectopic pregnancies.

D. Absence of a fetal heartbeat is a crucial sign to rule out an ectopic pregnancy, as a normal intrauterine pregnancy would have a fetal heartbeat. However, absence of a fetal heartbeat does not guarantee an ectopic pregnancy, as it may be absent in a missed or early miscarriage or intrauterine non-viable pregnancy.

**Clinical Pearl:** A combination of intrauterine gestational sac, fetal heartbeat, dilated uterine cavity, and normal endometrial thickness are crucial ultrasound signs to confidently rule out ectopic pregnancy.

**Correct Answer:** D. Absence of a fetal heartbeat indicates that there is no fetal heart activity, which can be indicative of an ectopic pregnancy. However, this alone is not sufficient, as mentioned above, as it can be absent in other conditions as well.

**Why Each Wrong Option is Incorrect:**

A. Identification of an intrauterine gestational sac and dilated uterine cavity are not sufficient to rule out ectopic pregnancy, as these signs can also be present in intrauterine pregnancies that are missed or miscarried.

B. Absence of an intrauterine gestational sac is incorrect because an ectopic pregnancy may still present with an empty uterus (absence of gestational sac) but not necessarily rule out ectopic pregnancy, as it can occur in an empty uterus due to other reasons like missed or miscarried intrauterine pregnancy.

C. A normal endometrial thickness is not a guarantee for ruling out ectopic pregnancy, as