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Few women can experience symptoms suggestive of early pregnancy as early as 24 hours after fruitful intercourse. If pregnancy is suspected, look out for development of any other new symptoms suggestive of pregnancy. Wait and watch for your next periods. If periods do not start within 10 days of expected period dates, or if you get abnormal periods, or if you suspect chances of pregnancy, consider visiting your doctor/gynecologist at the earliest for thorough examination (to confirm pregnancy related changes/signs in body) and blood/serum HCG level test (to confirm/rule out pregnancy accurately).
Take care.