Thanks for the query.
I understand your concern.
In case of previous three regular menstrual cycles, expected date of delivery can be calculated by using last menstrual period date.
Dating scan at around 9 to 11 weeks can help in assessing the expected date of delivery.
A combination of these two gives a more accurate due date.
Means if both dates are correlating, that can be considered as more accurate date.
If periods are irregular, last menstrual period date may not give accurate due date and with progression of gestation, ultrasound may not give more accurate date.
These Q&A’s are for educational purposes and should not be relied upon as a substitute for medical advice you may receive from your physician. If you have a medical emergency, please call 911. These answers do not constitute or initiate a patient/doctor relationship.