Online calculator to determine the duration of pregnancy by ultrasound results. Measurement of embryo length allows you to determine the gestational age with great accuracy. It is necessary to know the duration of pregnancy to determine the duration of labour, to monitor the development of the fetus, to determine the duration of maternity leave.
The earlier the ultrasound is done, the more accurate it is at estimating the baby’s due date.
Ultrasounds performed during the first 12 weeks of pregnancy are generally within 3 – 5 days of accuracy.
The most accurate time is between 8 and 11 weeks gestation. This is because the fetus is growing so quickly that there is a big difference in size from week to week.
Also, the fetus cannot bend and twist too much yet, so the length of the body is fairly constant.
However, the accuracy of the ultrasound examination is always dependent on the skill of the sonographer and the quality of the equipment.
The scan or my dates – which should I believe? Usually, the expected date of delivery (EDD or EDC) is calculated from your last menstrual period – if the early dating scan calculates the EDD to be within 5 days of the EDD from your last menstrual period.
The EDD from the early dating scan is used – if the last menstrual period is not known or is unreliable, or the dating scan differs from the last menstrual period dating by more than 5 days.
As the baby gets bigger, it starts to express its individual growth potential.
The size of the baby correlates less and less with its age as time goes on.
Ultrasound examinations from 12 to 22 weeks are regarded as being within 10 days of accuracy (or up to 10 days earlier or 10 days later than the woman’s calculated due date).
Ultrasounds performed after 22 weeks gestation cannot be used to estimate the due date of the baby because the size no longer reflects the age very well. Even average babies can differ by up to 2 to 3 “weeks of growth”;. These scans are only used to estimate the due date of your baby if this is all you have to go on.
If you have more than one ultrasound during your pregnancy, giving you ‘multiple dates’, then the earliest ultrasound estimate should be used, because it will be more accurate.
If you have any questions about this, please feel free to talk to your sonographer or doctor about it.