Ultrasound accuracy for dating
Standard Ultrasound – Traditional ultrasound exam which uses a transducer over the abdomen to generate 2-D images of the developing fetus .Advanced Ultrasound – This exam is similar to the standard ultrasound, but the exam targets a suspected problem and uses more sophisticated equipment.
In the past, the EDC was calculated by using Naegele's Rule, which determined the date by subtracting 3 months from the 1st day of the last period and then adding 7 days.
Of all of these uses, dating the pregnancy is the most common reason to use ultrasound, particularly when the expectant mother cannot remember the date of her last period (as in breast-feeding or irregular cycles).
Even when the last period is known, ultrasound is reassuring to demonstrate adequate growth, especially when there’s a risk of delayed growth, as in hypertension or smoking, or if there’s the risk of exaggerated growth, as in gestational diabetes.
At 4.5 to 5 weeks, a gestational sac may be seen in the uterus using transvaginal ultrasound, Joseph Woo, M.
Ultrasound has become so helpful that obstetricians now refer to the time before it was used routinely as “the olden days.” We use it to diagnose twins early on; we use it to document appropriate growth as the pregnancy progresses; we use it to determine fetal health; and we use it to guide conversion of breech to vertex (head-first) position and to guide amniocentesis.