Dating a Pregnancy

Last updated 25.08.13



-  An agreed estimated due date (EDD) made as early as possible in pregnancy

-  To prevent assumed post dates: IOL, T/F for TPL, elective LUSCS


-  US

-  CRL on early frist trimester ultrasound (<14/40) most accurate method

-  Earlier is more accurate, can be measured from 6/40

-  AC most accureate estimator at later gestations

-  LMP

-  If early US result not available, or US at >14/40

-  If dates differ by >1 week use US result

-  9 months + 7 days

-  If regular 28 day cycle

-  If oligomenorrhoea, lactational amenorrhoea or OCP withdrawal bleeding use first US result