New Placenta Previa Definitions Advocated.

SAN FRANCISCO -- Which pregnant women need a double set-up exam for placenta previa?

That depends on both how placenta previa is defined and the degree of previa, Dr. Melinda M. Scully Noah said at a meeting on antepartum and intrapartum management sponsored by the University of California, San Francisco.

Variations in terminology can lead to confusion when interpreting ultrasound results. For example, some radiologists might define a marginal placenta previa as the placental edge being at the cervical stroma, but many obstetricians may think of it as the placental edge at the internal os.

Quantitative, unambiguous terminology being adopted by physicians at the University of California, San Francisco, should help predict which patients will need a C-section because of bleeding before or during labor, said Dr. Scully Noah, a fellow in maternal-fetal medicine at the university.

"Many of you are probably in practices where your ultrasounds are done at a different site, and you may or may not get to see the images. We're trying to improve the characterization of the placental location," she said. That move should help determine when to prepare a patient scheduled for a cervical exam to palpate the placenta for a possible emergency C-section if she starts bleeding during the exam.

Dr. Scully Noah and her associates in the radiology department compared use of the classic terminology with their new definitions (see box) in a retrospective chart review of data on 80 patients who gave birth at the university over a 4-year period. All had ultrasounds at 13 weeks' gestation or later that either did not rule out previa or showed incomplete previa.

Women whose ultrasounds showed complete previa--with placental tissue completely covering the internal os--were not included in the study because it was assumed they would undergo a C-section.