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| birth defect* |
retrieval set includes coverage of birth defect or birth defects |
| birth defects and folic acid |
retrieval set includes content covering birth defects and folic acid in the same document |
| birth defects or folic acid |
retrieval set includes either content covering birth defects or content covering folic acid |
| birth defects not folic acid |
retrieval set includes content that covers birth defects where folic acid is not covered in the document |
| (neural tube defects or birth defects) and folic acid |
retrieval set includes content where either neural tube defects or birth defects is covered and prevention with folic acid is covered in all content |