Ultrasound accuracy for dating
With transvaginal ultrasound, checking for embryonic development known to occur within a certain time frame more accurately dates a pregnancy.
Transvaginal ultrasound can see embryonic development about a week before transabdominal ultrasound, the American Pregnancy Association (APA) states.
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).
A transducer, a wand-shaped probe, is inserted into the vagina and pressed against the vaginal walls directly next to the uterus.
) the fetus is clearly seen on trans-vaginal ultrasound and the heart beat can be seen at this early stage (90 to 110 beats per minute under 6 to 7 weeks, then 110 to 200 beats per minute as the baby matures).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.