<prompt> Gestational sac is seen on TVS as early as :18 days from LMP21 days from LMP35 days from LMP42 days from LMP  <response>: An intrauterine gestational sac is visualised with transvaginal sonography by 5 weeks of gestation, and an embryo with cardiac activity by 6 weeks. The embryo should be visible transvaginally once the mean sac diameter has reached 20mm.Cardiac motion is usually visible with transvaginal imaging when the embryo is 5mm. Reference: williams Textbook of obstetrics 24th edition page no 196. 