title: Reply.
authors.affiliation: Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, TX 75235-9032. Electronic address: Elaine.Duryea@UTSouthwestern.edu.
authors.forename: Elaine L
authors.initials: EL
authors.lastname: Duryea
authors.affiliation: Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, TX 75235-9032.
authors.forename: Donald D
authors.initials: DD
authors.lastname: McIntire
authors.affiliation: Department of Obstetrics and Gynecology, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, TX 75235-9032.
authors.forename: Kenneth J
authors.initials: KJ
authors.lastname: Leveno
mesh_terms: D005260:Female; D005865:Gestational Age; D006801:Humans; D008297:Male; D008598:Menstruation; D011247:Pregnancy; D047928:Premature Birth / Q000453:epidemiology*; D016216:Ultrasonography, Prenatal