Pregnancy dating ultrasound calculator
The LMP formula is good for working out an initial age of pregnancy but ultrasound is more accurate.
Pregnancy is normally counted from a woman's last menstrual period which is about two weeks before baby is actually conceived.
Generally obstetricians or physicians initially calculate pregnancy from your last period without adjusting for an irregular cycle length.
This initial estimation may then be superseded or confirmed by an ultrasound.
Just 4% of babies are born on their due date while 70% are born within 10 days of the estimated due date.
The remaining 30% are born more than 10 days before the due date or more than 10 days after the due date.
This date will also have a /- number of days giving an accuracy range.