The 7-4 ruling by the full 8th Circuit Court of Appeals reversed a decision by a three-judge appellate panel in September 2011 that had ruled unconstitutional the suicide advisory provision in South Dakota's 2005 law.

The panel, which had upheld much of the law that set out what a pregnant woman should be told 24 hours before undergoing an abortion, had said a link between abortion and suicide was unproven and may not exist. South Dakota's governor and attorney general and two crisis pregnancy centers appealed.

The appeals court ruled on Tuesday that conclusive proof of a causation was not required and the suicide advisory was not misleading and was relevant to the patient's decision.

"Today's decision supports the Legislature's goal of encouraging women seeking an abortion to make informed and voluntary decisions," South Dakota Attorney General Marty Jackley said in a statement.

Planned Parenthood, the only abortion provider in South Dakota, was "extremely disappointed" by Tuesday's ruling, said Sarah Stoesz, president of Planned Parenthood Minnesota, North Dakota, South Dakota.

"This ruling by the 8th Circuit Court represents the greatest intrusion by the government into the patient-doctor relationship to date," Stoesz said in a statement.

Judge Raymond Gruender wrote in a 27-page opinion that a multitude of studies published in peer-reviewed medical journals have found an increased risk of suicide for women who had received abortions compared to women who gave birth, miscarried or never became pregnant.

"Various studies found this correlation to hold, even when controlling for the effects of other potential causal factors for suicide, including pre-existing depression, anxiety, suicide ideation, childhood sexual abuse, physical abuse, child neuroticism, and low self-esteem," Gruender wrote.

Four judges dissented from the decision on Tuesday, finding that the suicide advisory violates the patient's due process rights and violates a doctor's right against compelled speech.

"The most reliable evidence in the record shows that abortion does not have a causal relationship to the risk of suicide and that South Dakota's mandated advisory is not truthful, but actually misleading," Judge Diana Murphy wrote.

South Dakota has been at the center of some of the most bitter recent fights over abortion, which was legalized in 1973 by the U.S. Supreme Court in Roe v. Wade.

South Dakota was the first state to have what is sometimes called an informed consent law and has the most expansive law that has been imitated in part in other states including North Dakota, Missouri, Kansas and Indiana, according to the Guttmacher Institute, which studies reproductive health issues.

Jackley said Tuesday's ruling would provide guidance for challenges to South Dakota laws approved in 2011 and 2012.

South Dakota last year mandated the longest waiting period in the nation at 72 hours and a meeting at an anti-abortion counseling center before a woman could undergo the procedure, both challenged by Planned Parenthood.

Planned Parenthood had contended the suicide advisory imposes an undue burden on abortion rights and violates the free speech rights of the physician.

"That requirement really flies in the face of the science," Elizabeth Nash, public policy associate at the Guttmacher Institute, said on Tuesday of the suicide advisory.

Nash said extensive reviews, particularly by the American Psychological Association, have found no link between negative mental health outcomes and a single abortion for the average woman.

(Reporting by David Bailey in Minneapolis; Editing by Cynthia Osterman and Stacey Joyce)

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