- Patients with an accurately dated singleton gestation. Accurate dating is defined as estimated date of delivery (EDD) based on last menstrual period (LMP) dating (280 days after the first day of the LMP) confirmed by an ultrasound done before 20 weeks, which yields an EDD within 10 days of LMP dating. If the LMP is not available, the EDD must be based on 2 ultrasounds performed at least 2 weeks apart, which are concordant within 5 days of the same EDD.