Usually po nagbi base sila sa first ultrasound(trans v). Estimated lang naman po yan, pwede paren po kayong manganak 1 to 2 weeks before or after your EDD. Basta maka 37weeks pwede napo since fullterm na si baby that time :)
as per my OB po transv ultrasound daw po ang susundin, December 16 transv ko, pero sa pelvic December 10 👶👶