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The yolk sac is an organ of increasingly recognized importance in the initial mechanisms of pregnancy maintenance and the early growth and welfare of the embryo. Having a complex protein secretion and an equally intricate ultrastructure, it is the primary source of blood and germ cells. This small and to date largely ignored structure may have a vital and interesting part to play in human embryonic development, which may be comparable to its proven evolutionary importance in other animals. The aim of our study was to assess the vascularity of the yolk sac and vitelline duct in 105 patients between the 6th and 10th weeks of gestation who were scheduled for termination of pregnancy for psychosocial reasons. The patients were divided in five subgroups depending on the duration of gestation. All of them had a normal developing pregnancy with no clinical symptoms of pathology (e.g. bleeding in early pregnancy). Gestational age was calculated from the first day of the last menstrual period and substantiated by crown-rump (CRL) measurements. After exploration of the gestational sac and embryo by transvaginal sonography, color Doppler was used to image the yolk sac and vitelline duct vascularity. The visualized vessels were analyzed with pulsed Doppler using the sample volume unit set of 1 mm. The assessment of obtained waveform signals was made by means of peak systolic Doppler shift (PSV) and pulsatility index (PI). The pulsatility index was calculated as a difference between peak systolic and end diastolic Doppler shift divided by the mean maximum velocity. At least 5 separate cardiac cycles were measured, and the mean value was calculated.(ABSTRACT TRUNCATED AT 250 WORDS)

Vascularization of yolk sac and vitelline duct in normal pregnancies studied by transvaginal color and pulsed Doppler