Ultrasound demonstration of the normal fetal yolk sac

Abstract

Using high-resolution real-time ultrasound in the first trimester of pregnancy, we have been able to demonstrate, in addition to the fetus, the yolk sac and the amniotic membrane. Pitfalls to avoid in first-trimester pregnancies include (a) mistaking the yolk sac for a second separate fetus, (b) including the yolk sac in the crown-rump length, and (c) misinterpreting the amniotic membrane for a septum between two separate gestational sacs.

Normal First Trimester of Pregnancy

“…Presence of fl uid between the fetal chin and chest can be used as a sign to ensure that the fetus is not hyperfl exed [ 2 ]. In practical terms, prior to 7 weeks gestation, measurement is actually of the longest length of the embryo that can be seen, but, after 7 weeks, a concerted effort should be made to measure the embryo in the midsagittal plane, excluding the with narrowed sector width is able to detect a circular echogenic ring, which represents the yolk sac ( white arrow ) and thus confi rms an early IUP yolk sac [ 38 ] (Fig. 7.7c ).…”

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

“…1 This sac, which represents the chorionic cavity, is a small anechoic fluid collection surrounded by an echogenic ring that represents trophoblasts and decidual reaction. 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.…”

“…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.…”

Intrauterine membranes: Sonographic findings and clinical significance

“…With careful scanning techniques, segments of the unfused amniotic membrane can be demonstrated in normal pregnancies after seven weeks' menstrual age. 4 The amnion is composed of five tissue layers-a single layer of epithelium and four layers of connective tissue.' The entire membrane is firmly adherent to the cord; however, the fifth, or deepest layer is only loosely attached to the chorion, forming a potential space into which amniotic fluid dissects easily at delivery.…”