Hormone replacement therapy may negatively impact your fertility (for instance, in people with testes it can reduce sperm count and motility) but it doesn’t necessarily make you infertile. Post-pubertal trans people may be able to come off cross-sex hormones to enable sperm/egg production to resume. However, to mitigate the possible impact on future fertility post-pubescent trans people will typically be offered fertility preservation before starting hormones in the form of freezing sperm or eggs.