First Trimester Ultrasound

Abstract

The fi rst trimester of pregnancy is a time of literally amazing developments when a single fertilized ovum transforms into a recognizable human fetus in 13 weeks. The high-resolution images from state-of-the-art sonography can reliably detect the number of gestational sacs, embryos, and fetuses present, and complications such as anembryonic pregnancies or pathologic lesions that can occur in the fi rst trimester. These sonographic fi ndings, when used with concurrent laboratory data and the clinical examination, may determine the viability or nonviability of the pregnancy at a single setting, and, furthermore, provide reassurance in most cases of viability. Normal Sonographic First Trimester DevelopmentThe fi rst trimester, by convention, begins 2 weeks after fertilization of the oocyte (assumed to be 4 weeks after the fi rst day of the last normal menstrual cycle) and concludes 12 weeks later. Many key items of information can be obtained during either a routine or an urgent fi rst trimester ultrasound, including gestational age assessment, viability confi rmation, and screening for embryonic or fetal anomalies. For patients who have an uncertain last menstrual period, fi rst trimester ultrasound serves the critical role of establishing the accurate gestational age. Once established, gestational age then serves as the reference point for the growth and development of the fetus. In a patient with a positive pregnancy test and vaginal bleeding, or other signs or symptoms, the ultrasound can help to determine viability of the pregnancy by comparing the current products of conception with expected gestational age-matched fi ndings.For patients with an uncertain last menstrual period, fi rst trimester ultrasound serves the critical role of establishing the accurate gestational age.The earliest feature to indicate intrauterine pregnancy by ultrasound is the gestational sac, and its measurement is used to determine the gestational age. At its earliest detectable V o l u m e 3 8 • N u m b e r 2 J a n u a r y 1 5 , 2 0 1 5 Lippincott Continuing Medical Education Institute, Inc., is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians. Lippincott Continuing Medical Education Institute, Inc., designates this enduring material for a maximum of 2 AMA PRA Category 1 Credits™. Physicians should only claim credit commensurate with the extent of their participation in the activity. To earn CME credit, you must read the CME article and complete the quiz and evaluation on the enclosed answer form, answering at least seven of the 10 quiz questions correctly. This continuing medical education activity expires on April 13, 2015. Dr. Cooke is Radiology Resident,The authors and all staff in a position to control the content of this CME activity and their spouses/life partners (if any) have disclosed that they have no relationships with, or fi nancial interests in, any commercial organizations pertaining to this educational activity. CME Category: Women's Imagin...