Hi,
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The chances of pregnancy cannot be 'predicted' as percentage. If she was in her fertile days (as confirmed by her details of having fertile mucus) at time of sexual contact and if pre-cum (it is known to contain sperms in it) or semen has come in direct contact with vagina, then, the chances of pregnancy resulting are high. There are no studies to prove that sperms can swim through fabrics (unless it is thin and lightly woven and there is ample vaginal wetness). If you suspect direct contact with semen or pre-cum at any time during your sexual contact, and if you are not ready for baby you she should consider taking emergency contraception within 48 hours of the unprotected intercourse to prevent pregnancy. Wait and watch for her next periods. If you intend to remain sexually active, she should consider visiting her gynecologist to get started on suitable regular birth control measures to be protected (after her periods). She should be regular with birth control use as instructed to remain protected. Avoid having unprotected sexual contact.
Take care.