However, Charles E. Vignetta of the Johns Hopkins Bloomberg School of Public Health said he also found studies with the most flawed methodology found negative mental health conditions related to abortion.

The researchers examined studies dealing with the potential association between abortion and long-term mental health outcomes published from Jan. 1, 1989, to Aug. 1, 2008, and reviewed 21 studies that met the inclusion criteria. Studies were rated as excellent, very good, fair, poor, or very poor, but no study was rated excellent.

The 21 analytical studies had sample sizes ranging from 120 to 133,950; with maximum follow-up of 25 years. Populations studied came from seven countries and participants spanned the reproductive age range -- 12 to 54.

Claims that women who have elective abortions will experience psychological distress, or a "post-abortion syndrome" akin to post-traumatic stress disorder, has fueled debate on abortion, however, the existence of such an abortion-related syndrome has yet to be established empirically, Vignetta said.

The review, published in the journal Contraception, found lingering post-abortion feelings of sadness, guilt, regret and depression appear to occur in a minority of women.