Ultrasound accuracy in dating pregnancy
There is always a chance the urine test kit you are using is defective and cannot accurately detect HCG in your urine.
Consider buying a different brand and retest your urine if you think your results are wrong.
Consult your doctor if you are concerned about your results.
Your pregnancy test is wrong if you get a negative result even though you are actually pregnant (false negative) and a positive result when you are not (false positive).
The following are the main reasons for an inaccurate pregnancy test result.
A conception in the uterus that is lost in the early days of implantation, such as a chemical pregnancy, might initially give a positive test.
When the pregnancy becomes nonviable, usually because of the failure of implantation, the low level of HCG might still be detectable on a blood test for a short while.
The abnormal pregnancy makes lower levels of HCG, which might be slow to detect.
The HCG level can subsequently increase and become detectable though more slowly than with a normal pregnancy.