Dec. 14, 2010 -- Women who have regular mammograms should consider paying attention to when they are scheduled. New research finds the timing of mammograms could affect the accuracy of results.
''Try to schedule it during the first week of your menstrual cycle," says researcher Diana Miglioretti, PhD, a senior investigator at Group Health Research Institute in Seattle, who led the study. "The first day of your menstrual cycle is the day you start to bleed."
But she adds: "I don't want women to stress too much over this, if they can't get in."
Her study does show, however, that timing of mammograms can make a difference for women who regularly get them. For some reason, the timing did not seem to have the same effect on accuracy in the women studied who were getting their first mammogram, Miglioretti tells WebMD.
The study is published online in the journal Radiology.
Previous studies have looked at the timing of mammograms, Miglioretti says. Some experts have found that accuracy might be better in the first half of the cycle.
Other research has shown that breast density may be lower during the first half of the cycle. "We know breast density strongly affects mammography performance," she says. If a woman has a lot of dense tissue, it's more difficult to find cancer.
Timing of Mammograms: Study Details
Miglioretti and her colleagues examined 387,218 mammograms from women aged 35 to 54 who got the screenings from 1996 through 2007. The data were retrieved from six National Cancer Institute-funded Breast Cancer Surveillance Consortium mammography registries.
In all, 1,283 of the mammograms were linked to breast cancer cases.
The researchers took into account when the women had the mammograms and whether it was their first or not. They found that for women who had already had a screening mammogram in the past two years, the sensitivity -- the number of true positive findings -- was highest in those who had the mammograms the first week of their cycle. ''It was about 80% the first week," Miglioretti says.
By weeks two, three, and four, it was 67% to 73%. Put another way, Miglioretti tells WebMD, ''it raised the chance of catching the cancer 7 to 13 percentage points" by having the mammogram during week one of the cycle.
They found no effect of the timing of mammograms on false positives -- when you get called back for something that looks suspicious but turns out to be nothing to worry about.
''It's a little bit surprising," Miglioretti says, "because breast density is associated with false positives."
Then came another surprise: women who were having their first screening mammogram and had it during the first week of their cycle had less sensitivity than if they scheduled it later in the cycle. It's not clear why.