Ay, good question! From what I've learned with my pregnancies and from a few of my mum friends, usually ang ultrasound mo sa second trimester ang mas accurate para sa due date kasi mas clear pa ang dating ng baby non, pero honestly better to ask your OB directly because bawat case ay iba-iba depende sa dating and development ng baby mo, sila ang makakaalam best kung alin talaga ang gagamitin nila for your records. Congrats on your pregnancy!