As per my OB, first 6 months pareparehas ng development ang babies. When you reach 3rd trimester, dun possible na kahit 34 weeks ka na based sa LMP pero si baby 33 weeks parin kaya may ibang edd na lalabas sa ultrasound. Pero as per the rule of thumb daw ng mga OB. They will always refer to the EDD based sa LMP :-)