Hi,
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The Pullout/withdrawal method of contraception is associated with highest failures (it is known to contain sperms and no man can be 100% sure that pre-cum/ pre-ejaculatory fluid did not leak out during vaginal penetration). If she was during her fertile days, or closer to her ovulation time (time of egg release from ovary), then chances of pregnancy are possible. She can consider taking emergency contraceptive within 24-48 hours of the unprotected intercourse to prevent pregnancy. Since these pills contain high hormonal dosages, there can be period and menstrual cycle abnormalities including delay in periods. Avoid further unprotected sexual contact. If pregnancy gets ruled out, and if you are not ready for pregnancy, but intend to remain sexually active, she should consider visiting her gynecologist to get started on suitable regular birth control measures to be protected (after the periods). She should be regular with birth control use as instructed.
Take care.