[1] Univ Maryland, Dept Obstet Gynecol & Reprod Sci, Baltimore, MD 21201 USA
[2] Univ Hamburg Eppendorf, Dept Obstet & Prenatal Med, Hamburg, Germany
[3] Univ Colorado, Hlth Sci Ctr, Dept Obstet & Gynecol, Denver, CO 80202 USA
[4] St George Hosp, Sch Med, Fetal Med Unit, London, England
[5] Univ Bonn, Dept Obstet & Prenatal Med, D-5300 Bonn, Germany
[6] Leiden Univ, Dept Obstet & Gynecol, Leiden, Netherlands