1. Department of Anesthesiology, University of Michigan, Ann Arbor, MI, USA;
2. Department of Obstetrics and Gynecology, Oakland University William Beaumont School of Medicine, Royal Oak, MI, USA;
3. Taubman Health Sciences Library, University of Michigan, Ann Arbor, MI, USA;
4. Department of Obstetrics and Gynecology, University of Michigan, Ann Arbor, MI, USA