Hello, Thank you for your question. A missed period is often the first clue that a women might be pregnant. Sometimes, a woman might suspect she is pregnant even sooner. Symptoms such as headache, fatique, and breast tenderness, can occur even before a missed period. All pregnancy tests work by detecting a special hormone in the urine or blood that is only there when a woman is pregnant. It is called human chorionic gonadotropin or hCG. hCG is made when a fertilized egg implants in the uterus. hCG rapidly builds up in your body with each passing day you are pregnant. Blood tests can pick up hCG earlier in a pregnancy than urine tests can. Blood tests can tell if you are pregnant about about six to eight days after you ovulate. Doctors use two types of blood tests to check for pregnancy. Quantitative blood test for beta hCG test measures the exact amount of hCG in your blood. So it can find even tiny amounts of hCG. This makes it very accurate. Qualitative hCG blood tests just check to see if the pregnancy hormone is present or not. so it gives a yes or no answer. This blood test is about as accurate as a urine test. Your symptom can be belong to pregnancy if you are sure that you are pregnancy. Talk to your doctor about what kind of blood test that your doctor check for test pregnancy. Hope I have answer your question. Let me know if I can assist you further. Best regards, Dr. Heang Chan Raksmey, General and Family physician.