BIOL 171 Lecture Notes - Lecture 18: Yolk Sac, Gestational Sac, Decidua
Document Summary
The gestational period is broken into trimesters: 1st trimester week 1-12, 2nd trimester weeks 13-26, 3rd trimester weeks 27-40. This is the first structure visualized within the gestational sac: us appearances round sonolucent structure with echogenic rim, size = 4mm, transvaginally non-visualization of the yolk sac when msd is greater than 8mm abnormal! Normally seen about 5 weeks from lmp: transabdominally non-visualization of yolk sac when msd is greater than 20mm = abnormal! If the yolk sac is not visualized in the gestational sac and the gestational sac measures 8mm then there is most likely a problem. Blighted ovum embryo has died and been restored or was never present: fhm/fhb. If no fhm is detected, the sonographer and radiologist (or obstetrician) must watch for cardiac activity for 3 minutes! Most important measurement for 1st trimester: sac diameter, length, width, crl = crown rump length, heartbeat, normal for 1st trimester = 120-170 bpm.
