If the quality criteria for CRL measurement before 14 weeks are not met, the date pregnancy began should be determined by the date of the last menstrual period and the usual duration of the
patient’s cycles. This rule does not apply to pregnancies by IVF, for which the date pregnancy began is defined by the date of oocyte retrieval (Professional consensus). Before any intervention for
prolonged pregnancy, it should be verified that the best indicators were used for dating the pregnancy: date of oocyte retrieval, CRL with its quality criteria, or date of last menstrual period (Professional consensus).