Pregnancy Dating

Pregnancy Dating

• EDD is "set by" a sure LMP or an ultrasound. ie) "EDC set by sure LMP of 2/4/15"

• EDD is "confirmed by" an u/s if it matches LMP (less than discrepency as listed below). ie) EDC is confirmed by 19 wk u/s"

• EDD is "changed by" an u/s if discrepency supports redating. ie) "EDC is changed by 12 wk u/s"

If you are changing an EDD make sure you have thoroughly reviewed the chart and any other ultrasounds.

PLEASE, PLEASE, PLEASE don't change an EDC in a chart unless you know for sure that it should be changed and if you change it, be sure to document. If it is unclear, ask.

Estimating gestational age

• • Ultrasound measurement of the embryo or fetus in the first trimester (up to and including 13 6/7 weeks of gestation) is the most accurate method to establish or confirm gestational age.

  • If pregnancy resulted from assisted reproductive technology (ART), the ART-derived gestational age should be used to assign the estimated due date (EDD). For instance, the EDD for a pregnancy resulting from in vitro fertilization should be established using the age of the embryo and the date of transfer.

  • As soon as data from the last menstrual period (LMP), the first accurate ultrasound examination, or both are obtained, the gestational age and the EDD should be determined, discussed with the patient, and documented clearly in the medical record. Subsequent changes to the EDD should be reserved for rare circumstances, discussed with the patient, and documented clearly in the medical record.

  • When determined from the methods outlined in this document for estimating the due date, gestational age at delivery represents the best obstetric estimate for the purpose of clinical care and should be recorded on the birth certificate. For the purposes of research and surveillance, the best obstetrzic estimate, rather than estimates based on the LMP alone, should be used as the measure for gestational age.