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If fertile mucus had been present at time of intercourse, sperms can stay alive for 5-7 days and fertilize the egg upon ovulation. After ovulation, egg has only 24-48 hours to get fertilized. If she was during her fertile days at time of intercourse, chances of pregnancy are possible due to pre-cum coming in contact with vagina. She should consider taking emergency contraception within 48 hours of intercourse if she is not ready for pregnancy (and if she is during her fertile days). She should consider visiting her doctor/gynecologist for further evaluation if she develops any other symptoms, or if periods/withdrawal bleeding does not start within 10 days of expected period date. Treatment as appropriate (based on examination findings and investigation results) would be started to help her regulate her periods. If you are not ready for pregnancy, but intend to remain sexually active, you should consider getting her started on suitable regular birth control measures to be protected (after her periods). She should be regular with birth control use as instructed. Avoid having unprotected sexual contact if you are not ready for pregnancy.
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