What are the consequences of missing birth control pills a lot?

Pregnancy & Bleeding: Birth control pills work best when taken at the same time everyday, without missing any. Studies have shown that many women are late in taking their pill or miss 1 - 3 pills per month. At the best, abnormal bleeding can occur. At the worst, especially if you miss the first several pills in the pack, an unintended pregnancy can occur. If this is your pattern, may consider changing your method.