What is the chance of getting a false negative on pregnancy test at possible 16 weeks of pregnancy?

Hmmm...: Most women know they are 16 weeks pregnant without a urine or blood test. So, if there is an obvious baby inside, then any negative pregnancy test is a false negative. That being said, a false negative pregnancy test is rare after 4-5 weeks of pregnancy... which means that if a woman has not "confirmed a pregnancy" at 16 weeks, and she gets a negative test result, she should visit her doctor.