The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk. At the end of the fourth week the yolk-sac presents the appearance of a small pear-shaped vesicle (umbilical vesicle) opening into the digestive tube by a long narrow tube, the vitelline duct.


The fetal pole is a thickening on the margin of the yolk sac of a fetus during pregnancy. It is usually identified at 6.5 weeks with abdominal ultrasound imaging, and 6 weeks with vaginal ultrasound imaging. However it is quite normal for the fetal pole to not be visible until about 8 weeks.


Crown-rump length (CRL) is the measurement of the length of human embryos and fetuses from the top of the head (crown) to the bottom of the buttocks (rump).
A decidual reaction can be observed in tissue of the peritoneum and ovary during a pregnancy, and represents a response of stromal tissue to progesterone.


Given the data you provided (6wks 6days pregnant), the results on the ultrasound imaging are what is expected. The sonographer might have not been able to visualize the yolk sac and it is absorbed within time when the placenta is formed to replace the circulatory role of the yolk sac.


According to the gestational age the fetal heart beat is expected to be approximately 126 at the start of week 7 and 149 bpm at the end of week 7.


You might want to talk with a gynecologist or fetal ultrasound specialist/sonographer for an additional explanation of the results.