A guide to choosing an alternative form of contraception

A night of unexpected passion, a failed attempt at contraception — sometimes it happens. Consider an IUD, or perhaps you need emergency contraception: a pill (or pills) containing the same hormones found in birth control pills but in a higher dose. Here's some information on alternative contraceptives to help you choose the best option.

No. These pills won't prevent all pregnancies.

• Researchers aren't sure exactly how it works. Studies suggest the pills interrupt ovulation, but it's not clear whether they have any effect on the fertilization or implantation of the egg.
• Progestin-only pills are 89 percent effective if started within 72 hours of unprotected intercourse; combination pills that include estrogen are 75 percent effective.
• How effective emergency contraception is for you may depend on where you are in your menstrual cycle when you take it. For best results, emergency contraception should be taken within 24 hours of unprotected intercourse (as the hours pass, the pill becomes less effective).
• Main side effects include nausea and vomiting. In the case of the latter, you may need another dose. Nausea and vomiting are less common with progestin-only pills.

More than 80 percent of women use oral contraceptives during their lifetimes, and many never even consider other options. But studies show that due to human blunders (like forgetting to take one of your pills), oral contraceptives are only up to 97 percent effective compared to a 99 percent effectiveness rate for intrauterine devices, or IUDs.

• Although not especially popular, modern IUDs are a safe and effective form of reversible contraception.
• An intrauterine device (IUD) is a small T-shaped piece of flexible plastic that's implanted by a doctor into a woman's uterus.
• Some IUDs are hormone-free. The ParaGard IUD is a piece of plastic wrapped with copper. It can be left in place for up to 10 years. It's unclear how it works, but it does.
• A second type of IUD continuously releases a small amount of the hormone progestin, which thickens the cervical mucus so sperm can't get through. It also reduces the frequency of ovulation and thins the endometrium. This type can be left in place for up to five years.
• Recent studies debunk many women's fears that IUDs cause pelvic infections or sterility. But the devices do come with an unpleasant side effect: more bleeding. One German study of 1,466 women found that up to 65 percent of IUD users experienced heavier, prolonged and more painful periods after an IUD was inserted.

Another method, the vaginal ring, which is inserted into the vagina and releases estrogen and progestin to protect against pregnancy, is just as effective as oral contraceptives but provides lower exposure to hormones, more consistent estrogen levels and better control over menstruation, according to Swedish research.

With so many options available, it can be difficult to find the right form of contraception. Consider this guide and contact your gynecologist to find a contraception that works.