[1] Univ Maryland, Sch Med, Dept Obstet Gynecol & Reprod Sci, Baltimore, MD 21201 USA
[2] Univ Maryland, Sch Med, Dept Epidemiol & Publ Hlth, Baltimore, MD 21201 USA
[3] Univ Maryland, Sch Med, Dept Pediat, Baltimore, MD 21201 USA
[4] St Johns Mercy Med Ctr, Dept Obstet & Gynecol, Baltimore, MD USA
[5] MedStar Harbor Hosp, Dept Obstet & Gynecol, Baltimore, MD USA