A pregnancy blood test can typically detect pregnancy 6–8 days after ovulation, which is usually 7–12 days before a missed period. This early detection window is possible because blood tests measure human chorionic gonadotropin (hCG), a hormone produced by the placenta, at much lower levels than urine tests can detect.
The timing depends on several factors. After conception, the fertilized egg travels down the fallopian tube and implants in the uterine lining, a process that takes about 6–12 days. Once implantation occurs, hCG begins to be produced and enters the bloodstream. Blood tests can detect hCG levels as low as 1–2 milli-international units per milliliter (mIU/mL), while home urine tests typically require 20–25 mIU/mL or higher.
For the most reliable results, healthcare providers recommend waiting until the first day of a missed period or later, when hCG levels are higher and less likely to produce false negatives. However, many people successfully detect pregnancy with a blood test several days before a missed period.
There are two types of blood tests: quantitative hCG tests (which measure the exact hormone level and can detect lower concentrations) and qualitative hCG tests (which simply confirm whether hCG is present or absent). The quantitative test is more sensitive and can pick up pregnancy earlier.
If you test too early, you may get a false negative, so repeating the test a few days later is often recommended if you're testing before your missed period and get a negative result but still suspect pregnancy.