Vaginal Ultrasound Dating Accuracy & Fetal Growth - Expert Advice

Question
hello. from united states..

i read all over the net, but i wanted a experts advice..
if my vaginal ultrasound dated me at 3.14cm exactly 10 weeks 0 days. do i count back 8 weeks for conception date..?? july 30th was that date...
also are vaginal ultrasound more accurate than abdomen ones??

also in your clinic.. at what age do they fetus start to grow at different rate..

thanks so much!


Answer
Dear Tyra

Vaginal ultrasound can be more accurate than abdominal only in some indications such as very early pregnancy and genital tumors. Your calculatoion for the date of conception is accurate from the theoritical point. However, most ultrasound machines have a falacy of 2 weeks. This means that ultrasound may show 11 or 12 weeks pregnancy which is actually 10. Similarly, a pregnancy of 10 weeks may show on ultrasound as 8 or 9 weeks The 2 weeks margin may go up or down.

The growth of the fetus varies according to geographical location, your altitude relative to the see, ethnic group and some other factors. Generally speaking the fetus have (more or less) constant pattern of growth till 12 weeks, then it changes between 13-28 and then a 3rd change may occur till delivery.

Good Luck