Hi XXXXXXX

Thanks for the query.

It is the ultrasound scan which gives the growth of the fetus and the estimated fetal age(not an ECG).This scan is done at the early days of pregnancy, and is known as "Dating Scan".

The scan is done routinely to determine the expected date of delivery (EDD). We generally consider the dating scan results as accurate in determining EDD. These calculated dates are usually one or two weeks plus or minus the dates as calculated through Naegele's formula (through Last Menstrual Period)

EDD calculated from the date of intercourse or fruitful coitus will have a lag of one to two weeks from the expected date as calculated from the date of last menstrual cycle. Implying Date of intercourse may not be correlating with the scan dates mentioned.

So, the prediction of the age of the fetus/gestational weeks lies best with the ultrasound scan reports , then the calculations made by dates of fruitful intercourse or last menstrual periods.

Hence it is expected that some changes in dates are possible, do not worry about it as long as the baby is growing fine and scan reports are normal

Hope I answered your query, I will be available for follow ups as well.

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