It can detect lower levels of HCG and confirm or rule out pregnancy earlier than a urine test. Even if you haven't missed a period, a blood test can reveal pregnancy. Pregnancy blood tests are almost always correct. To confirm the findings of a home pregnancy test, a blood test is frequently performed. This test measures the level of human chorionic gonadotropin (HCG) in the blood. HCG is produced by the placenta and is found in high levels in pregnant women. HCG levels rise steadily throughout pregnancy and drop after pregnancy has been confirmed so a single test cannot determine whether you are still pregnant. Therefore, it's important to take follow-up tests at regular intervals after the first test results are known. Women who suspect they are pregnant but have not yet missed their period may find out for sure with a blood test. The sooner you find out if you're pregnant, the better your chances of keeping the baby. A blood test is the only way to be certain if you are pregnant because other tests don't show evidence of fetal development until much later. A blood test can also help rule out other conditions that may cause similar symptoms, such as endometriosis or hyperthyroidism. Endometriosis is when tissue that normally lines the inside of the uterus grows outside of it; this usually occurs after puberty when estrogen levels increase.