How Accurate Is My Due Date?
Your estimated date of delivery (EDD) was likely calculated by adding 240 days to the first day of your last menstrual period (LMP). This calculation assumes that you menstruate every twenty-eight days but if your cycle is generally shorter or longer, your baby may arrive earlier or later. An ultrasound may also be used to predict your baby’s delivery date but in either case, the date predicted is an estimate only.1 Pregnancies vary and can last anywhere from thirty-seven to forty-two weeks because every pregnancy is different, just as labour triggers are. Studies show that most women give birth later than expected, and only 5% of women deliver on their predicted due date.2