Ah yes, usually pwede ka nang magpabp ultrasound kahit walang doctor's request, lalo na kung private clinic or hospital, bayad mo lang directly at pwede mo i-schedule agad! One of my mum friends did this during her pregnancy kasi gusto niya lang mag-checkup in between ng scheduled visits, so go ahead lang, pero sa totoo lang mas safe kung may guidance ng doctor para alam niya ano dapat i-check based sa kung saan ka na sa pregnancy.