IUD Beats Pill at Preventing Pregnancy

Birth Control Pill's Risk of Failure Is 20 Times More Than That of IUDs, Implants

Medically Reviewed by Louise Chang, MD on May 23, 2012

May 23, 2012 -- Women using birth control pills may have a 20 times greater risk of an unplanned pregnancy than women using longer-acting forms of birth control like an intrauterine device (IUD) or implant, new research shows.

A major new study shows the failure rate of birth control pills and other short-term prescription contraceptives is much higher than previously thought, based on how women actually use them in real life.

Researchers say the results call for a major shift in how women and health care providers think about birth control options.

"In medicine, whether you have stroke, hypertension, or diabetes, if you have a medication that is 20-fold less effective, would you offer it as first-line choice?" says researcher Jeffrey Peipert, MD, of Washington University in St. Louis.

Birth control pills are currently the most commonly used reversible form of birth control in the U.S.

Only about 5.5% of American women who use contraception use IUDs, compared with much higher usage rates in other developed countries like the U.K. and France.

Removing the 'Oops' Factor

Researchers say unplanned pregnancies are a major public health issue. Unplanned pregnancies can have a negative impact on women's health and education as well as the health of newborns.

Previous studies have shown that about half of the estimated 3 million unplanned pregnancies each year in the U.S. are the result of contraceptive failure.

Although short- and long-term birth control methods work slightly differently in terms of preventing pregnancy, Peipert says the main reason behind the much lower failure rate for the IUD and implant is the removal of the "oops" factor.

"These methods are forgettable," Peipert tells WebMD. "You don't have to remember to take a pill, get a shot, or put in a ring. They remove human factor in terms of human error."

How They Work

Hormonal implants work by slowly releasing hormone to prevent the ovaries from releasing eggs. They are inserted under the skin of the upper arm and are effective for up to three years. They are available as Implanon and Nexplanon in the U.S.

An IUD is a small "T" shaped device that is inserted into the uterus by a health care provider. It works by stopping sperm from making it through the vagina and uterus to fertilize an egg.

There are two types of IUDs available in the U.S., the Mirena hormonal IUD and ParaGard copper IUD. Both are more than 99% effective at preventing pregnancy for five to 10 years, depending on the device.

If taken exactly as directed, birth control pills are also more than 99% effective at preventing pregnancy.

But in reality, few women remember to take the pills at the same time every day to achieve these optimum results. The yearly failure rate with typical use is estimated to be 9%, but with younger women and high-risk groups the failure rate increases.

"There are also a lot of other barriers like getting refills, prescription renewals, and insurance coverage that comes and goes," says Sarah J. Betstadt, MD, MPH, assistant professor of obstetrics and gynecology at the University of Rochester. She was not involved in the study.

IUD Beats the Pill

Researchers say this is the first large study to compare the failure rate or number of unplanned pregnancies between users of IUDs or implants and short-term contraceptives, including birth control pills, patches, vaginal rings, and birth control shots.

After an initial consultation about birth control options, researchers provided 7,486 women of reproductive age with their choice of contraception free of charge.

During three years of follow-up, 334 unplanned pregnancies occurred. Of these, 156 pregnancies were due to failure of contraception provided during the study. The remaining unplanned pregnancies were due to failure of other forms of contraception not included in this study, such as condoms and withdrawal.

Researchers found that 133 women using pills, the patch, or ring experienced an unplanned pregnancy compared with 21 women who used IUDs or implants. Two women used birth control shots.

In addition, the risk of unplanned pregnancies among young women under age 21 using birth control pills, patch, or ring methods was twice as high as the risk among older women. The rates of unplanned pregnancy were similar between women using birth control shots and those using IUD or implant, regardless of age.

The results appear in the New England Journal of Medicine.

Cost a Major Issue

Experts say the study confirms IUDs and hormonal implants are better than birth control pills and other short-term contraceptives in preventing unplanned pregnancies.

"There has never been a large head-to-head comparison of pregnancy outcomes of women choosing different contraceptives," says Carolyn Westhoff, MD, senior medical advisor at Planned Parenthood. "The pill, patch, and vaginal ring are still good with a 95% success rate, but the pregnancies among IUD and implant users were vanishingly few."

Westhoff says the study is also remarkable because it shows that given the choice, women will choose these long-acting methods of birth control over the pill, patch, or ring.

"If you can take away the barriers of access and cost, large numbers of women will say, 'I want this most effective long-acting method,'" Westhoff tells WebMD.

Once cost was taken out of the equation, 75% of women in the study chose IUDs or implants for birth control.

The up-front costs for an IUD can range from $500 to $1,000. That means many health care providers do not keep them in stock, and many private insurance companies do not cover them.

But compared with the monthly costs of birth control pills, rings, and patches, as well as the higher risk of unintended pregnancy, Westhoff says IUDs are more cost-effective in the long run.

More Education Needed

On a smaller level, IUDs may still be suffering from an image problem. An early form of the IUD called the Dalkon Shield sold in the early 1970s was eventually recalled after it was linked to pelvic infections leading to infertility and even death in some cases.

But modern IUDs have a proven track record of safety. Peipert says today's IUDs have a low risk of infection, and the hormonal version may actually help protect against infection by thickening mucus in the uterus.

Betstadt says those myths and misconceptions about IUDs still persist among some health care providers, too.

"We need to educate not only women but health care providers as well," Betstadt tells WebMD.

"Whatever a woman wants to use is the best method for her," says Betstadt. "We want them to make a choice that works for them. But we should say to them that IUDs and implants are much more effective at preventing pregnancies."

The study was funded by the Susan Thompson Buffett Foundation.

Peipert reports receiving compensation for consultation and expert testimony for the defense regarding the association of clotting disorders associated with the vaginal ring. He has also received lecture fees from Omnia Education and lecture fees to his institution from Merck as a contraceptive implant trainer.

Show Sources


Winner, B. New England Journal of Medicine, May 24, 2012.

Jeffrey Peipert, MD, vice-chair for clinical research, department of obstetrics and gynecology, Washington University School of Medicine, St. Louis.

Sarah J. Betstadt, MD, MPH, assistant professor, department of obstetrics and gynecology, University of Rochester Medical Center.

Carolyn Westhoff, MD, senior medical advisor, Planned Parenthood.

News release, Washington University School of Medicine.

CDC, MMWR, May 6, 1983.

Fu, H. Family Planning Perspectives, March/April 1999.

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