The use of transvaginal ultrasound allows for earlier evaluation of pregnancy than with transabdominal ultrasound. 

Evaluation of patients with early pregnancy is aimed at determination of viability of the pregnancy and at confirmation of correct placement in the uterus- an IUP (intrauterine pregnancy)

Typical landmarks expected to be seen include the following:

·         Development of a sonolucent area within the uterine cavity- this is the gestational sac and it is seen between 4-5 weeks which beta hCGs around 1500-2000

·         Until a yolk sac is noted within the gestational sac, one cannot confirm the presence of an IUP. 

o   Pseudogestational sacs can be seen in ectopic pregnancies.

o   A yolk sac should be seen by the time the gestational sac reaches about 5-8mm. 

o   Gestational sacs greater than 10mm without visible yolk sacs are of concern for ectopic pregnancy or for abnormal embryonic development.

·         The next developmental milestone noted is the fetal pole (around 6 weeks).  This should be found in gestational sacs greater than 18mm in diameter and if not present should be concerning for abnormal embryonic development.

·         The gold standard in diagnosing an IUP is the observation of fetal cardiac activity.

o   This should be expected shortly after 6 weeks and when the gestational sac is over 16mm

Heller and Jehle. Ultrasound in Emergency Medicine

http://www.sonoguide.com/obgyn.html

Linda Regan, MD FACEP

Program Director, Emergency Medicine Residency

Johns Hopkins Medical Institutions