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: We investigated this association , according to the type of progestagen included in third - generation ( i . e . , desogestrel or gestodene ) and second - generation ( i . e . , levonorgestrel ) oral contraceptives , the dose of estrogen , and the presence or absence of prothrombotic mutations METHODS : In a nationwide , population - based , case - control study , we identified and enrolled 248 women 18 through 49 years of age who had had a first myocardial infarction between 1990 and 1995 and 925 control women who had not had a myocardial infarction and who were matched for age , calendar year of the index event , and area of residence .
### Output Text:
We investigated this association , according to the type of <span class="chemical">progestagen</span> included in third - generation ( i . e . , <span class="chemical">desogestrel</span> or <span class="chemical">gestodene</span> ) and second - generation ( i . e . , <span class="chemical">levonorgestrel</span> ) <span class="chemical">oral contraceptives</span> , the dose of <span class="chemical">estrogen</span> , and the presence or absence of prothrombotic mutations METHODS : In a nationwide , population - based , case - control study , we identified and enrolled 248 women 18 through 49 years of age who had had a first myocardial infarction between 1990 and 1995 and 925 control women who had not had a myocardial infarction and who were matched for age , calendar year of the index event , and area of residence . 