Does negative blood test 30 days after ntercourse rule out pregnancy?

Yes: Pregnancy tests are very accurate and not affected by foods, herbs, common illnesses, sexually transmitted diseases, or medications. A correctly done pregnancy test gives a reliable result 3 weeks after sex (3 weeks after when conception might have happened) or 1 week after missing a period. Also, if one's normal, regular menstrual period comes, then she is not pregnant.