OBSTETRIC ULTRASOUND IMAGING
Obstetrical ultrasound provides pictures of an embryo or fetus within a woman's uterus, as well as the mother's uterus and ovaries.
WHY IS THE PROCEDURE PERFORMED:
establish the presence of a living embryo/fetus
estimate the age of the pregnancy
diagnose congenital abnormalities of the fetus
evaluate the position of the fetus
evaluate the position of the placenta
determine if there are multiple pregnancies
determine the amount of amniotic fluid around the baby
check for opening or shortening of the cervix
assess fetal growth
assess fetal well-being
WHAT IS SEEN:
First trimester sonography can be performed transabdominally or transvaginally. Transvaginal imaging has better resolution and can visualize fetal structures earlier. The following information should be documented on routine exam in first trimester pregnancy:
intrauterine location of pregnancy
cardia motion on M-mode tracing
measurement of gestational sac
yolk sac or embryo for estimation of gestational age
number of gestational sacs/embryos
the adnexal structures.
A number of sonographic findings may indicate that a pregnancy will have a poor outcome. Some of these include the following:
abnormal gestational sac shape or size
lack of embryo in a large gestational sac
low position of a gestational sac within uterus
Ectopic pregnancy has a number of sonographic findings which can be seen both intrauterine and/or extrauterine. These findings are dependent on the location of the ectopic pregnancy, the gestational age, and the presence of hemorrhage due to rupture. Sonographic findings must be correlated with serum beta hCG levels.
LENGTH OF THE EXAM:
INTERPRETING THE RESULTS:
Obstetric ultrasound cannot identify all fetal abnormalities. Consequently, when there are clinical or laboratory suspicions for a possible abnormality, a pregnant woman may have to undergo nonradiologic testing such as a blood test or amniocentesis (the evaluation of fluid taken from the sac surrounding the fetus) or chorionic villus sampling (evaluation of placental tissue) to determine the health of the fetus, or she may be referred by her primary care provider to a perinatologist (an obstetrician specializing in high-risk pregnancies).
IMAGES, TEXT, SOURCES, STUDIES:
Dunstan Abraham, Cynthia Silkowski, Charles Odwin-Emergency Medicine Sonography_ Pocket Guide to Sonographic Anatomy and Pathology-Jones & Bartlett Publishers (2009)