Girls, moms! I can't understand: every screening gives different indic…

Girls, moms! I can't understand: every screening gives different indicators for gestational age, and therefore the due date is not clear. For example, if we count by ultrasound, such terms: 1st screening: 31 week 5 days 2nd screening: 31 week 2 days 3rd screening: 32 weeks 4 days By menstrual cycle (irregular): 33 weeks 2 days. On the last screening they said that the large fetus, and naturally the BPR is big, tfu-tfu no deviations. And what should I believe in and rely on????? ????