Placenta praevia--a review with emphasis on the role of ultrasound.
Considerable confusion exists in the literature as a result of the wide range of classification systems for placenta praevia (PP) and low-lying placenta. The discrepancy between frequency of low-lying placentas in the second trimester and PP at term reflects to a certain extent the lack of understanding of the anatomy and physiology of the pregnant uterus. It seems that 'placental conversion' is a real phenomenon and is probably due to the differential growth rates of the placenta and uterus. Maternal bladder overdistension and myometrial contractions account for only a small part of the discrepancy. Diagnostic ultrasound obviously has an important role in placental localization. The role of Magnetic Resonance Imaging remains to be determined. The management of patients with low-lying placenta diagnosed in the second trimester, and the frequency of repeat scans is determined largely by the management protocol of the attending obstetrician.
Langlois
S L
SL
Flinders Medical Centre, Flinders University of South Australia, Adelaide.
Miller
A G
AG
D005260:Female; D006801:Humans; D010923:Placenta Previa / Q000145:classification / Q000175:diagnosis* / Q000453:epidemiology; D011247:Pregnancy; D014463:Ultrasonography