THURSDAY, Feb. 23 (HealthDay News) -- Hormonal contraceptives
appear to thwart pregnancy just as well in overweight and obese
women as those of normal weight despite markedly lower
pregnancy-prevention hormone levels among heavier females, a group
of reproductive experts said.
During a media briefing held Thursday by the Planned Parenthood
Federation of America and the Society of Family Planning,
researchers said few large studies on contraception have included
obese women, creating gaps in knowledge about the safety and
effectiveness of various methods among this population.
About one-third of all American women between ages 20 and 39 are
obese, and most of these women will use contraception, said Dr.
Vanessa Cullins, vice president of external medical affairs for
Planned Parenthood Federation of America.
"Obesity and unintended pregnancy are two of our major health epidemics, and this is at the intersection of both," Cullins said. "Armed with additional information, we hopefully will be at a place where we can give more detailed and customized advice to women who are overweight or obese."
New findings presented Thursday indicated that
pregnancy-prevention hormone levels varied widely among obese and
normal-weight women using Implanon, a contraceptive implant that
works for up to three years. These hormone levels ranged between 31
and 54 percent lower in obese women, whose body mass index (BMI) is
30 or higher, said study author Dr. Melissa Gilliam, a professor of
obstetrics and gynecology, and pediatrics at the University of
BMI is a measurement that takes both height and weight into
"Obese women had a much slower time to reach peak [blood] levels -- 100 hours versus 50 -- and these were never as high as in normal-weight women," said Gilliam, also board president of the Society of Family Planning, adding that the study did not determine whether these women were more likely to become pregnant while using the method.
Weight gain, another concern among hormonal contraceptive users,
was addressed in a study of young women using the Depo-Provera
contraceptive shot, which is administered every 12 weeks. It found
that those who gained significant weight within six months of
starting the shots had higher levels of certain enzymes in their
fat cells before they even began.
However, "The majority of women are not at risk for large
increases in weight while using [Depo-Provera]," said study author
Dr. Andrea Bonny, an assistant professor of pediatrics at
Nationwide Children's Hospital in Columbus, Ohio. "Future studies
need to better identify the differences in fat cells between those
that do and don't gain weight."
Another study, on rhesus monkeys, found that birth control pills
were not linked to weight gain among female primates and actually
triggered weight loss among those who were obese. However,
scientists note that research involving animals often fails to
produce similar results in humans.
Study author Dr. Alison Edelman, an associate professor in the
department of obstetrics and gynecology at Oregon Health and
Science University in Portland, also presented findings from
separate research suggesting that birth control drug levels were
lower among obese women -- especially after the seven-day pill
break coinciding with users' menstrual periods.
In theory, obese women might be more vulnerable to pregnancy
during this time period, but Edelman noted that a recent study of
52,000 women found only slight differences in oral-contraceptive
failure rates between obese and normal-weight women.
"These differences aren't sufficient enough to overcome the overwhelming benefits achieved by women finding the method that works best for them," she said.
In an era of increasingly customized medicine, the researchers
said more data would help doctors to better tailor contraceptives
to overweight and obese women.
Edelman referred to long-term methods such as hormonal implants
and intrauterine devices (IUDs) as the "Cadillac of products" for
women of any weight, but said she and other experts don't have yet
enough information to recommend that obese women currently alter
their usage of hormonal contraceptives.
"Contraceptives are usually studied in a normal-weight population . . . but we're changing our one-size-fits-all philosophy," Edelman said.
The Association of Reproductive Health Professionals has more on
how hormonal contraception prevents
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