"People are always worried about weight gain whenever you mention a hormone, even though weight gain is miniscule in our experience," Rabin said. "But I don't think we've answered the question, certainly not with the LNG, and not even with oral contraceptives."
Many women in the study received Kaiser insurance through work, Kwock said. Otherwise they were diverse and probably representative of the women nationwide, she added.
Kwock and study co-author Dr. Julie Livingston looked at a number of factors in the Kaiser medical records of these women, such as weight, age, race, medical conditions that might cause them to gain weight (such as diabetes and thyroid disease) and whether they were taking an antidepressant.
They found no differences for any of these factors between LNG and copper IUD users.
In addition, weight loss, albeit small, seemed to be similar between the LNG and copper IUD users; however this result might not be real, Kwock again cautioned.
Many women start on an IUD after they have had a baby, so Kwock and Livingston compared the proportion of women in each group who had received their IUD within two months of childbirth but found no differences.
The weight loss that the researchers saw in each group was not just due to the fact that some of the women were losing their "baby fat", Kwock said.
"A lot of the doctors we work with really recommend IUDs for new moms because they are busy and they don't have time to remember to take pills," Kwock said.
"One of my favorite forms of birth control is the LNG because it has so many benefits -- women get lighter periods and have less cramping, while the copper IUD can actually make periods more heavy," Kwock said.
However, some patients prefer copper IUDs and it really depends on the patient, Rabin said.
More than with IUDs, women really worry about gaining weight on the pill,
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