Ay mama, ganyan talaga ang nangyayari, the transv ultrasound is usually more accurate early on kasi nakikita ng doctor ang exact measurements ng baby, pero once you're further along like now, the margin of error gets bigger, so the OB's dating using the transv reading makes more sense. I'd say follow your OB's assessment since sila ang nakakita ng lahat ng details during your ultrasound and they know your case best, pero you can always ask your doc to explain the difference between the two dates para peace of mind mo!