Yes, you can become pregnant if you start a new pack of birth control without using backup contraception, particularly during the first week. Birth control pills require consistent use to maintain effectiveness—missing pills or starting late reduces protection immediately. If you begin a new pack after a break or miss the first few pills, sperm can fertilize an egg during that vulnerable window. The first week of a new pill pack is considered the highest-risk period because hormone levels haven't built up sufficiently in your system to prevent ovulation reliably. Most medical guidelines recommend using a backup contraceptive method (condoms, abstinence) for the first seven days when starting a new pack, especially if there was a gap between packs. Other birth control methods like patches, rings, and injections have similar timing concerns. If you're concerned about a potential pregnancy risk, take a pregnancy test if your next period is late, and discuss your contraceptive routine with a healthcare provider to ensure you're using your method correctly for maximum protection.