title: Timing of mid-trimester sacral ossification.
authors.forename: Nicholas M
authors.initials: NM
authors.lastname: Fisk
authors.forename: Isabel
authors.initials: I
authors.lastname: Shirley
mesh_terms: D000328:Adult; D005260:Female; D047109:Fetal Development / Q000502:physiology*; D005865:Gestational Age; D006801:Humans; D008875:Middle Aged; D010012:Osteogenesis; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D012447:Sacrum / Q000000981:diagnostic imaging / Q000196:embryology*; D013997:Time Factors; D016216:Ultrasonography, Prenatal / Q000379:methods*