It can usually be detected by pregnancy test one week after the fertilized egg has been laid, but ultrasound is needed to further determine if the pregnancy is intrauterine. A pregnancy test can be performed one week after the fertilized egg has been laid, usually using a pregnancy test strip to detect HCG levels in the urine (i.e., human chorionic gonadotropin), or in the blood, and a positive test indicates a high likelihood of pregnancy. A positive pregnancy test should be followed by a note that an ultrasound is needed for further confirmation, as some of the elevated HCG may be indicative of a biochemical pregnancy. Therefore, patients are advised to monitor urine HCG or blood HCG one week after conception to determine if they are pregnant and to seek medical attention if there are any abnormalities.