Ay, totally normal yan first-time mom, hindi ka nag-iisa with this! The ultrasound measurement is usually more accurate than LMP, lalo na if your cycle was irregular or you're not 100% sure of your exact dates, kaya follow mo nalang ang ultrasound dating na 17 weeks para consistent sa baby's actual development. A few of us had the same thing happen, and honestly, doctors use the ultrasound to adjust the due date pa lang, walang life-threatening issue usually, pero best talaga to mention it sa OB mo next visit para ma-clarify and she can explain kung bakit may difference and monitor properly moving forward!