About 99% of women went ahead with an abortion after voluntarily viewing an ultrasound image of the fetus beforehand, according to a large new U.S. study, Fox News reports.

Based on medical records for more than 15,000 women seeking abortion at Los Angeles Planned Parenthood clinics, researchers found that only a small fraction of the women changed their minds after seeing the image.

Ten states have enacted laws that require doctors to perform ultrasounds before abortions, and three of those require the woman to view the image during the ultrasound. 

Advocates for ultrasound laws base the requirement on the idea that showing a woman the image of her fetus might cause her to have a change of heart about terminating the pregnancy.

The researchers reviewed medical records from 15,575 visits at 19 Planned Parenthood clinics in Los Angeles during 2011. These facilities routinely perform ultrasounds before abortion procedures and regularly ask the patients if they want to see the images. It's also standard practice to ask each patient how confident she is about her decision to terminate the pregnancy.

Responses to both of these questions are noted in the patient's electronic medical record, according to the researchers. Katrina Kimport at the University of California San Francisco School of Medicine and her colleagues analyzed those records and found that most women (85.4 percent) said they were certain they had made the right decision to have the abortion. A smaller number (7.4 percent) were classified as having medium or low levels of certainty about getting the procedure.

Although all of the women included in the study had ultrasounds, less than half (42.5 percent) chose to see the image.

A total of 98.8 percent of the planned abortions took place. Among women who did not view their ultrasounds, 99 percent went through with the procedure. Among those who did view the images, 98.4 percent of the women had abortions.

The images appeared to have the greatest effect among women who had expressed low or medium certainty about the procedure. In that group, those who viewed the ultrasounds were slightly less likely to go through with the abortion: 95.2 percent did have the procedure, compared to 97.5 percent of uncertain women who did not view the ultrasound.

Women who expressed high certainty about their decision showed no differences, whether or not they had viewed the ultrasound.