We sought to review the risks of placenta accreta, increta, and percreta, and provide guidance regarding interventions to improve maternal outcomes when abnormal placental implantation occurs.Relevant documents were identified through a search of the English-language literature for publications including ≥1 of the key words "accreta" or "increta" or "percreta" using PubMed (US National Library of Medicine; January 1990 through January 2010); with results limited to studies involving human beings. Additional information was obtained from references identified within selected articles; from additional review articles; and from guidelines by organizations including the American College of Obstetricians and Gynecologists. Each included article was evaluated according to study design and quality in accordance with the scheme outlined by the US Preventative Services Task Force.Abnormal placentation--encompassing placenta accreta, increta, and percreta--is increasingly common. While randomized controlled trials and large observational cohort studies that can be used to define best practice are lacking, strategies to enhance early diagnosis, enhance preparation, and coordinate peripartum management can be undertaken. Women with a placenta previa overlying a uterine scar should be evaluated for the potential diagnosis of placenta accreta. Women with a placenta previa or "low-lying placenta" overlying a uterine scar early in pregnancy should be reevaluated in the third trimester with attention to the potential presence of placenta accreta. When the diagnosis of placenta accreta is made remote from delivery, the need for hysterectomy should be anticipated and arrangements made for delivery in a center with adequate resources, including those for massive transfusion. Intraoperatively, attention should be paid to abdominal and vaginal blood loss. Early blood product replacement, with consideration of volume, oxygen-carrying capacity, and coagulation factors, can reduce perioperative complications.