Third trimester na ung ultrasound mo Kaya hindi namagandang pagbasehan Yan. Kasi ung utz Naka base Yan sa timbang at height ng baby.. If sure ka sa huling regla MO na calculate na NG center ir lying in Yan so mga last week ng January Yan.. Pero 2 weeks before and after ng due date mo is considered normal.. So ibig sabihin Mag ready kna mommy pwede Kang manganak anytime from 3rd week of January to 2nd week ng feb