Christian pro-life groups are calling a new study which claims a controversial abortion pill is safe as misleading because it avoids comparing women who use the pill to women who have never had an abortion.

The study on the medical-abortion drug mifepristone, commonly referred to as RU-486, appeared in the August 16 issue of the New England Journal of Medicine, and concluded that RU-486 is safe - at least in the long run.

But it was coverage from TIME magazine that made the study more widely known.

TIME pointed out that the new study contradicted an earlier study published in 2003 in the American Journal of Epidemiology, which found a link between medical abortion and a nearly threefold greater risk of ectopic pregnancy - a condition where the fertilised egg implants itself outside the uterus and can cause the death of the mother.

Millions worldwide have used RU-486 to end their pregnancy. In comparison, nearly 1.3 million undergo surgical abortion a year, according to TIME.

The study used the abortion and pregnancy data of more than 11,600 women from the Danish National Patient Registry to compare the impact of using drugs versus surgery on women's long-term reproductive health.

As the magazine pointed out, the study simply showed that women using RU-486 were at the same risk-level of those choosing surgical abortion. It did not compare the reproductive health of women who had drug-induced abortions or surgical abortions to those who did not have an abortion.

"Reporters are drawing the erroneous conclusion that this study means RU-486 is completely safe. That's not what the study says, and nothing could be further from the truth," said Cheryl Sullenger, senior policy advisor of the US-based Christian pro-life group Operation Rescue, in a statement Thursday.

"Women who have had abortions have greater risks of miscarriage and infertility than women who have not had abortions," said Sullenger. "It is no accident that the study refused to compare these two groups of women, because we know they would have found that abortion hurts women, and that is obviously a conclusion that they did not want to reach."

RU-486 was approved by the Food and Drug Administration in 2000, but its image was ruined when several cases of deaths from use of the pill were reported. Seven women died - six in the United States and one in Canada - after using mifepristone and misoprostol together or misoprostol alone between 2003 and 2006. Mifepristone terminates the pregnancy while misoprostol causes uterine contractions to expel the pre-born baby.

"This study is no comfort to the families of Holly Patterson, Vivian Tran and Chanelle Bryant who, among others, died believing that they would survive an RU-486 abortion," said Carrie Gordon Earll, senior bioethics analyst for Focus on the Family Action.