Can transvag us miss a pregnancy if last intercourse was 9 weeks beforehand? had two normal periods after that but now third one is late

Ultrasound pregnancy: Transvaginal ultrasound will not miss a pregnancy of 8 weeks gestation. If dating is incorrect even after 4 weeks a sac should be seen by ultrasound.

Maybe...: Transvaginal u/s is unlikely to miss a 9 week pregnancy in the uterus. If the pregnancy is not in the uterus, it could be missed. The best thing to do is get a blood pregnancy test. It will pick up a pregnancy no matter where it is. Best wishes!