1. Division of Maternal Fetal Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA;
2. Department of Obstetrics and Gynecology, University of Michigan, Ann Arbor, MI, USA;
3. Department of Obstetrics and Gynecology, Case Western Reserve University, Cleveland, OH, USA;
4. Division of Maternal Fetal Medicine, Oregon Health & Sciences University, Portland, OR, USA;
5. Division of Maternal Fetal Medicine, Duke University, Durham, NC, USA