Hindi talaga exact, mama! Even sa ultrasound, kita lang nila kung gaano kalaki ang baby based sa size, pero hindi siya pinaka-accurate, maybe off by a week or two pa. A few of us tried asking our OBs kung exact ang date, pero sabi nila mahirap talaga kasi ang dating ng ovulation at fertilization ay may variation, lalo na kung irregular ang cycle mo. Best bet is yung dating scan in first trimester, pero take it as approximate lang para peace of mind.