3 weeks after embryo transfer with a positive pregnancy test but no sac on ultrasound.Is this possible or is it too early to do an ultrasound?

It is possible to have a positive pregnancy test but not see a sac on an ultrasound at 3 weeks after embryo transfer. This is because it can take some time for the gestational sac to develop and become visible on ultrasound. The best time to see the gestational sac on ultrasound is between 5 and 6 weeks after embryo transfer. If you have not seen a sac on ultrasound by this time, it is important to talk to your doctor. They may want to repeat the ultrasound or perform other tests to rule out any potential problems.