Biometry Guidelines for Re-dating
As a routine, use date provided by the clinicians or patient’s known LMP. Change dates only if there is a significant discrepancy between the clinical dates and the dates calculated by US (ALWAYS NOTE IN YOUR DISCUSSION IF YOU CHANGED DATES THAT WERE PROVIDED).
Significant discrepancy for various gestational ages is as follows:
1st trimester (up to 14 weeks) – > 1 week
2nd trimester (up to 27 weeks) – > 2 weeks
3rd trimester (> 27 weeks) – > 3 weeks
After the 1st trimester, if the dates are discrepant and 1st trimester US is not available, change dates after discussion with the clinicians or make a note in the report that the dates were changed. As a rule do not change dates, in the third trimester unless instructed by the clinicians.
2nd trimester dates can be used if 1st trimester US is not available, no clinical information is available and the dates are discrepant.
Cerebellar size is more accurate in cases with discrepant growth and absent anomalies. Please make sure that the cerebellum is measured in all cases.
DO NOT CHANGE DATES IN AN IVF PATIENT.
If there is discrepancy between dates by US and clinical dates, please add the following to the impression:
“The dates obtained by US are discrepant with the dating suggested by LMP/clinical dates. Re-dating should be considered.”
Authors:
Manjiri Dighe, MD
Tom Easterling, MD