Hi Hcg is detected in blood  after 11 days of conception and in urine after 12 to 14 days. In around 80%of pregnancies hcg doubles up in 48 to 72 hours. Usually levels less than 5 mIU/ml is considered as negative and above 25 is considered as pregnancy. However an ultrasound scan at 4 to 5 weeks would be more ideal. Hope you are convinced. Best wishes