Contraceptives Work Well in Obese Women, But Hormone Levels Lower

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 Chicago.

BMI is a measurement that takes both height and weight into
account.

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.

More information

The Association of Reproductive Health Professionals has more on how
hormonal contraception prevents pregnancy
.

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