if you mean po is tvs ultrasound(transviganal ultrasound)may ipapasok sa vagina nyo na usually ginagawa during first trimester to check kung may heartbeat na,ilang weeks o Kung may problem na kailangan icure as soon as possible .And CAS(Congenital Anomaly Scan)nman is to check kung normal ang lahat sa magiging baby mo,dun malalaman kung mgkakabirth defect sya like cleft lip atbp.