A close look at early embryonic development with the high-frequency transvaginal transducer

SOGC Clinical Practice Guidelines: Ultrasound Evaluation of First Trimester Pregnancy Complications

“…2 With transvaginal ultrasound, it is possible to identify the sac by 4 weeks and 3 days gestation when the mean diameter is 2 to 3 mm. 1,3 The yolk sac is the first structure seen within the gestational sac 2 and, when seen, confirms an intrauterine pregnancy. The yolk sac is seen by transvaginal ultrasound when the mean gestational sac diameter is 5 to 6 mm and should always be visualized when the mean gestational sac diameter is greater than or equal to 8 mm.…”

“…1 Cardiac activity immediately adjacent to the yolk sac indicates a live embryo but may not be seen until the embryo measures 5 mm. 3,4 From 5.5 to 6.5 weeks, an embryonic heart rate of less than 100 beats per minute is normal. During the following 3 weeks, there is a rapid increase up to 180 beats per minute.…”

“…The yolk sac is seen by transvaginal ultrasound when the mean gestational sac diameter is 5 to 6 mm and should always be visualized when the mean gestational sac diameter is greater than or equal to 8 mm. 3 The amnion is a thin, rounded membrane surrounding the embryo and is completely enveloped by the thick echogenic chorion. The yolk sac is situated between the amnion and the chorion.…”

“…The amnion grows rapidly during pregnancy and fuses with the chorion between 12 and 16 weeks of gestation. 1,3 The embryo can be identified by transvaginal ultrasound when as small as 1 to 2 mm in length. At 5 to 7 weeks, both the embryo and gestational sac should grow 1 mm daily.…”

“…The yolk sac is seen by transvaginal ultrasound when the mean gestational sac diameter is 5 to 6 mm and should always be visualized when the mean gestational sac diameter is greater than or equal to 8 mm. 3 The amnion is a thin, rounded membrane surrounding the embryo and is completely enveloped by the thick echogenic These guidelines reflect emerging clinical and scientific advances as of the date issued and are subject to change. The information should not be construed as dictating an exclusive course of treatment or procedure to be followed.…”