An estimated 9 out of 100 women taking combination birth control pills will get pregnant in the first year of use. With perfect use as directed, the pregnancy rate is less than 1 in 100 women every year.

Although taking combination birth control pills during early pregnancy doesn't increase the risk of birth defects, it's best to stop them as soon as you suspect you're pregnant. Combination birth control pills won't protect you from sexually transmitted infections.

Combination birth control pills can cause side effects such as:

  • Breakthrough bleeding or spotting — more common with continuous-dosing or extended-cycle pills
  • Breast tenderness
  • Elevated blood pressure
  • Headaches
  • Nausea
  • Bloating

Some side effects — including nausea, headaches, breast tenderness and breakthrough bleeding — might decrease with continued use.

Combination birth control pills increase the risk of certain conditions, which can be serious. They include:

  • Blood clots in the legs
  • Heart attacks and stroke, especially if you smoke
  • Liver disorders
  • Gallbladder disease

Consult your health care provider as soon as possible if you're taking combination birth control pills and have:

  • Abdominal pain
  • Breast lump
  • Chest pain
  • Depression
  • Difficulty speaking
  • Eye problems, such as blurred or double vision or loss of vision
  • Fainting
  • Jaundice — yellowish discoloration of the skin
  • New or worsening headaches
  • Seizures
  • Severe allergic skin rash
  • Severe leg pain or swelling
  • Severe mood swings
  • Two missed periods or signs of pregnancy