Yes, it is not recommended to do an ultrasound scan in the fifth week of pregnancy because it is possible to see the gestational sac without an embryo. This is because the embryo is still very small and can lead to confusion. On the other hand, the empty gestational sac already makes one suspect that it may be an anembryonic pregnancy, known as a blighted ovum. The woman will have to repeat the ultrasound a few weeks later to check if there is any problem with the pregnancy.