Hi,
I am wondering about the accuracy of ultra sound in determining due dates.
Any studies you could refer me to?
Thank you,
maria. By: maria

Not very. A first trimester ultrasound gives an estimated due date that is accurate within plus or minus 5 days, in other words, within a 10-day window. For this reason, the authors of the review cited below do not recommend changing a due date unless the ultrasound date disagrees by at least 2 weeks. The later it is done in pregnancy, the wider the window becomes. Second-trimester ultrasounds are plus or minus 8 days.

Otto C and Platt LD. Fetal growth and development. Obstet Gynecol Clin North Amer 1991;18(4):907-931.

As a sidenote, the NIH report from the March 2006 conference on elective c/sec concluded that elective c/sec at 39 weeks would not cause danger from respiratory problems. But because of the limitations of ultrasound technology, what is thought to be a 39 week gestation might actually be a 38 week gestation, a fact the report conveniently omits--not to mention that because of normal variation in all physiologic processes, some 39 week babies still don't have mature respiratory systems. As has been said, "When the fruit is ripe, it falls from the tree."

-- Henci By: Henci Goer