hCG usually starts to rise soon after implantation begins. In many pregnancies, it can be detected in the blood about 8 to 10 days after ovulation, which is usually around the time implantation has happened or shortly after.
After hCG first becomes detectable, it usually continues to rise quickly in early pregnancy. Urine tests may take a little longer to show a positive result because hCG generally appears in urine after it is already present in the blood. This is why testing too early can sometimes give a negative result even if pregnancy has started.
For many people, a home pregnancy test is more reliable after a missed period. Testing before then may be possible with sensitive tests, but the result can depend on ovulation timing, implantation timing, and how concentrated the urine is.
A blood test ordered by an OBGYN can detect lower levels of hCG and may be useful if there is uncertainty, pain, bleeding, a history of ectopic pregnancy, or fertility treatment. Avoid using medications or supplements to affect hormone levels unless they are prescribed.