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: CONCLUSIONS : Alterations in fetal biometric measurements were observed among the heavy drinkers only when they continued drinking after becoming aware of their pregnancies .
### Output Text:
CONCLUSIONS : Alterations in fetal biometric measurements were observed among the heavy drinkers only when they continued drinking after becoming aware of their pregnancies . 