**Core Concept**
The recurrence risk of an open neural tube defect (NTD) such as anencephaly in a subsequent pregnancy is influenced by the genetic and environmental factors contributing to the initial occurrence. Neural tube defects result from the failure of the neural tube to close during embryonic development, and the risk of recurrence is higher in families with a history of NTDs.

**Why the Correct Answer is Right**
The recurrence risk of an open NTD is significantly higher in families with a previous child affected by an NTD. Studies have shown that the risk of recurrence in siblings of an affected child is approximately 3-5%. This increased risk is thought to be due to genetic factors, with multiple genetic loci contributing to the susceptibility to NTDs. Additionally, environmental factors such as maternal folate deficiency, obesity, and certain medications may also play a role in the development of NTDs.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the recurrence risk is not as low as 1-2%. While the risk of recurrence is not 100%, it is significantly higher than this low estimate.

**Option B:** This option is incorrect because the recurrence risk is not as high as 20-30%. While the risk of recurrence is higher in families with a history of NTDs, it is not as high as this estimate.

**Option C:** This option is incorrect because the recurrence risk is not as low as 0-1%. While the risk of recurrence is not 100%, it is significantly higher than this low estimate.

**Clinical Pearl / High-Yield Fact**
It is essential to counsel couples with a history of NTDs about the increased risk of recurrence and the importance of taking folate supplements before and during pregnancy to reduce the risk of recurrence.

**Correct Answer:** C. 3-5%