if there is no concern, 1 beses ang TVS during 1st trimester. ako, 3× na TVS during 1st trimester. 1st- first prenatal check up to determine AOG. 2nd- to check reason of cramping. 3rd- to check if there are no more contractions. after that, ang next ultrasound ko ay CAS na, during 2nd trimester. after that, next ultrasound ay BPS during 3rd trimester.