title: Should a first trimester dating scan be routine for all pregnancies?
abstract: Accurate pregnancy dating is important for diagnostic and management decisions during pregnancy. Dating by last menstrual period is less reliable than dating by ultrasound, since the former has memory-related and other sources of inaccuracy. Dating by first trimester ultrasound, via the crown-rump length, has a 95% confidence range of ±5 days, slightly better than the ±8 days for dating by second trimester ultrasound at 14-20 weeks. This small difference appears to be too small to justify a routine first trimester scan for the purpose of dating the pregnancy.
authors.affiliation: Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, 75 Francis St., OBC-3-010, Boston, MA 02115. Electronic address: pdoubilet@partners.org.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Doubilet
mesh_terms: D005260:Female; D047109:Fetal Development; D005865:Gestational Age; D006801:Humans; D011237:Predictive Value of Tests; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011262:Pregnancy Trimester, Second; D015203:Reproducibility of Results; D016216:Ultrasonography, Prenatal / Q000379:methods* / Q000592:standards
keywords: First trimester; Gestational age; Last menstrual period; Second trimester; Ultrasound