Ay, normal yan! A few of us moms went through the same thing, the app counts from your last period, pero ang ultrasound ay mas accurate kasi nakikita nila talaga ang baby's measurements. Usually may slight difference lang ng 1-2 weeks, especially kung irregular periods mo or late ka kumilos ng test. Best to go with what the ultrasound says para sa due date mo, pero mas sure if you ask your OB directly kasi sila ang makakasabi ng exact reason ng difference!