The most reliable way to detect pregnancy is a home urine test, which is highly accurate from the first day of a missed period. For earlier or more precise detection, a healthcare provider can perform a blood test. Passing large blood clots during your period can be concerning, but it is often treatable. Common reasons include temporary hormonal imbalances, uterine fibroids, endometriosis, or adenomyosis. Occasionally, it can indicate an early pregnancy loss. While small clots are normal, frequently passing clots larger than a quarter warrant a routine visit to your doctor. They can help identify the exact cause and offer reassurance and guidance.