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The first study to compare the effectiveness of the birth control pill in women with marked weight differences has found that the pill works equally well in women with obesity and thinner women. This new finding by physician-scientists at NewYork-Presbyterian Hospital/Columbia University Medical Center refutes a long-held conviction among many doctors that the pill may not reliably prevent pregnancy in women who are overweight or obese.

With obesity a significant health issue in the United States — the U.S. government estimates that nearly 65 percent of adult women ages 20 and older are overweight or obese — the reliability of the birth control pill in this population is critical, especially since pregnancy itself is riskier among women with obesity.

"As a physician, I am relieved by the results of this study. When I prescribe oral contraceptives to my patients with obesity, I can feel confident that I am giving them something that will work," says principal investigator Dr. Carolyn Westhoff, professor of obstetrics and gynecology and director of the Division of Family Planning at Columbia University College of Physicians and Surgeons, and an obstetrician/gynecologist at NewYork-Presbyterian Hospital/Columbia University Medical Center.

In the study, published in the August issue of the journal Obstetrics & Gynecology, Dr. Westhoff and her colleagues did not rely, as previous studies had, on women's recollections of how much they may have weighed at a time when the pill had failed and they became pregnant.

"We wanted to study what was actually happening in the ovaries of women and not depend on memory, which is notoriously faulty," Dr. Westhoff says.

Dr. Westhoff and her colleagues designed a prospective study where 226 women of normal weight or who were overweight, and between the ages of 18 and 35, were randomly assigned to take either a lower- or higher-dose version of the pill. The researchers purposely used the different dose levels to assess whether heavier women required higher dosing, as has been previously believed.

After three or four months of using the oral contraceptives — the time it usually takes for a woman's body to acclimate to the pill — the women had multiple ultrasounds and blood tests to determine if ovulation was being suppressed. The goal of oral contraception is to suppress ovulation.

Of the 150 women who used the pill consistently, three of the 96 women with normal weight ovulated, as did one of the 54 women with obesity. The researchers also found that when women were not taking the pill regularly, they ovulated with greater frequency.

"Our findings strengthen the message to patients that the pill will only work if it is taken every day. Weight does not seem to have an impact on suppression of ovulation, but consistency of pill-taking does," Dr. Westhoff says.

Importantly, the lower-dose pill seemed to be as effective as the higher-dose pill in suppressing ovulation in women with obesity. This is a crucial finding because women with obesity are at greater risk for developing blood clots from taking either type of pill, although the overall risk is small.

"Knowing that the lower dose works as well as the higher dose will allow physicians to not only help women with obesity avoid unwanted pregnancies, but also protect them from the possible health risks associated with higher doses," Dr. Westhoff says.

"For a woman to fear relying on her oral contraceptive to prevent an unwanted pregnancy is a huge burden. This study should put those fears to rest," Dr. Westhoff says.

Study co-authors included Dr. Jodi P. Lerner of NewYork-Presbyterian Hospital/Columbia University Medical Center; Ms. Emma K. T. Benn, Ms. Elizabeth R. Mayeda, Ms. Myunghee Paik and Ms. Anupama H. Torgal of Columbia University Medical Center; and Dr. Frank Z. Stanczyk of the University of Southern California, Los Angeles.

The research was supported by grants from the National Institutes of Health; oral contraceptives were provided by Duramed Pharmaceuticals.

Columbia University Medical Center

Columbia University Medical Center provides international leadership in basic, pre-clinical and clinical research, in medical and health sciences education, and in patient care. The Medical Center trains future leaders and includes the dedicated work of many physicians, scientists, public health professionals, dentists, and nurses at the College of Physicians & Surgeons, the Mailman School of Public Health, the College of Dental Medicine, the School of Nursing, the biomedical departments of the Graduate School of Arts and Sciences, and allied research centers and institutions. Established in 1767, Columbia's College of Physicians and Surgeons was the first institution in the country to grant the M.D. degree and is now among the most selective medical schools in the country. Columbia University Medical Center is home to the largest medical research enterprise in New York City and state and one of the largest in the United States. Columbia University Medical Center is affiliated with NewYork-Presbyterian Hospital. For more information, please visit www.cumc.columbia.edu.

NewYork-Presbyterian Hospital

NewYork-Presbyterian Hospital, based in New York City, is the nation's largest not-for-profit, non-sectarian hospital, with 2,353 beds. The Hospital has nearly 2 million inpatient and outpatient visits in a year, including more than 220,000 visits to its emergency departments — more than any other area hospital. NewYork-Presbyterian provides state-of-the-art inpatient, ambulatory and preventive care in all areas of medicine at five major centers: NewYork-Presbyterian Hospital/Weill Cornell Medical Center, NewYork-Presbyterian Hospital/Columbia University Medical Center, NewYork-Presbyterian/Morgan Stanley Children's Hospital, NewYork-Presbyterian/The Allen Hospital and NewYork-Presbyterian Hospital/Westchester Division. One of the most comprehensive health care institutions in the world, the Hospital is committed to excellence in patient care, research, education and community service. NewYork-Presbyterian is the #1 hospital in the New York metropolitan area and is consistently ranked among the best academic medical institutions in the nation, according to U.S.News & World Report. The Hospital has academic affiliations with two of the nation's leading medical colleges: Weill Cornell Medical College and Columbia University College of Physicians and Surgeons.