In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: At the time of admission , the patient was at high risk of radiation injury to the fetus , so a coronary angiogram was postponed until the second trimester .
### Output Text:
At the time of admission , the patient was at high risk of radiation injury to the fetus , so a coronary angiogram was postponed until the second trimester . 