How early can ultrasounds detect pregnancy??

Using transvaginal ultrasound, the earliest sign of a pregnancy is the gestational sac, seen in the uterus. This can be seen as early as week 4. But, at this point, we cannot see if there is a fetus developing within that sac, as it is too small. A fetal pole can be seen by week 6.

''The gestational sac is the earliest sonographic finding in pregnancy...The gestational sac first appears at about 4 weeks gestational age..The yolk sac first appears during the fifth week of pregnancy..A mass of fetal cells, separate from the yolk sac, first becomes apparent on transvaginal ultrasound just after the 6th week of gestation.''

http://obgyn.ufl.edu/obgyn101/Ultrasound/1st_trimester_ultrasound_scannin.htm

They can usually see a sac in there by 6 weeks

With a good technician and hospital grade US machine the local hospital was able to locate the embryo at 5 weeks gestation ( i had went in with bleeding after a positive test)

an ultrasound can detect a viable pregnancy from approx 6wks,which is about 2 wks after you are expecting your period.

6 weeks,but they usually do it at 12-13 weeks

i had a transvaginal ultrasound which detected a 6 week old fetus