How accurate are early ultrasounds for conception dating
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.
Usually conception occurs 2 weeks prior to a missed LMP, but this is ONLY an estimate.
Later in the second trimester, you can be at least 2 weeks off.
If you were to present for your first sono in the third trimester there can be 3 or more weeks of uncertainty of dates. Read more Very premature is a condition in which a baby is delivered between 28 and 31 weeks' gestation.
The scans typically performed by your ob/gyn are often are more detailed to determine how your fetus and its anatomy are developing. Read more Onset of labor and delivery depends on multiple factors, mostly maternal, and estimates are that 10% of infants are born earlier than 37 weeks.
Age of mother, prenatal care, size and number of babies, uterine shape, maternal smoking or drugs, previous cervical cone biopsy and maternal infection are the most common. Read more The accuracy is plus or minus a week or so.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.