**Core Concept**
A chemical pregnancy refers to a very early pregnancy loss, typically occurring before the embryo implants in the uterus or before the gestational sac is visible on ultrasound. This condition is also known as a biochemical pregnancy or a pregnancy of unknown location.

**Why the Correct Answer is Right**
In a chemical pregnancy, the body produces human chorionic gonadotropin (hCG) in response to the implantation of a fertilized egg, but the pregnancy does not progress. Therefore, the beta hCG levels are positive, indicating the presence of a pregnancy. However, the gestational sac, which is the structure that develops into the placenta, is absent. This is because the embryo has not implanted successfully or has failed to develop. The presence of positive beta hCG and absent gestational sac is a characteristic feature of a chemical pregnancy.

**Why Each Wrong Option is Incorrect**
**Option A:** Negative beta hCG and absent gestational sac - This option is incorrect because a negative beta hCG would rule out pregnancy, whereas a chemical pregnancy is characterized by positive beta hCG levels.

**Option B:** Positive beta hCG and present gestational sac - This option is incorrect because a present gestational sac would indicate a normal pregnancy, whereas a chemical pregnancy is characterized by an absent gestational sac.

**Option D:** Negative beta HCG and created sac margin - This option is incorrect because it is unclear what "created sac margin" refers to, and it does not accurately describe the characteristics of a chemical pregnancy.

**Clinical Pearl / High-Yield Fact**
A chemical pregnancy is often asymptomatic and may only be diagnosed after a missed period or a positive pregnancy test. It is essential for healthcare providers to counsel patients about the possibility of a chemical pregnancy, especially in cases of recurrent pregnancy loss.

**✓ Correct Answer: C. Positive beta HCG and absent gestational sac**