When you take a pregnancy blood test after your period is late, it measures the levels of human chorionic gonadotropin (hCG) in your blood. If the test shows that you are "slightly pregnant," it means that there is a low level of hCG present in your bloodstream. This could indicate an early pregnancy or a very early miscarriage. It's important to consult with your healthcare provider for further evaluation and guidance. They may recommend repeating the test in a few days to monitor any changes in hCG levels or suggest additional tests like an ultrasound to confirm the pregnancy and assess its viability. Remember, only a healthcare professional can provide accurate information and advice based on your specific situation.