The absence of echoes in the uterus on day 42 of pregnancy suggests a possible pregnancy sac structure. Early gestational sac structure that is anechoic. Generally menstruation is more regular, in 42 days of pregnancy ultrasound can show the pregnancy sac, the pregnancy sac is amniotic fluid, so for the non-echo, round or round-like, the diameter of the gestational sac is usually about 10mm or so. If the menstrual period is often early, the yolk sac can also be observed growing out of the gestational sac. If there is no sound image of the gestational sac in the uterine cavity at 42 days, we should focus on observing the fallopian tube and ovary area bilaterally to see if there is a sound image of the gestational sac and to exclude the possibility of ectopic pregnancy. If there is no abnormality in the adnexal area bilaterally, the gestational sac is considered to be late in implantation, and you can wait for a few more days to review the ultrasound.