Fetal Femur Length Accuracy: Ultrasound Dating & Measurement

Question
hello
from louisiana, usa
i have had a 6 week ultrasound, 10 week, and 20week scan where doct measured and checked for kidneys,bladders etc... all my scans have dated me within two days. and i pretty much know when i conceived to within a day. the femur was measuring alil behind. the AC and BPD were right on target. after 20 weeks is the femur length the most accurate? or is the other two? ( all gave me due dates of 2-27-11 and 2-25-11 in the first trimester?
thanks
tara


Answer
Hello Tara from the U.S.,

The most accurate ultrasound for dating is at 7-9 weeks gestational age (margin of error 3 days).  At 20 weeks, the margin of error is 14 days for dating.

Good Luck,

Edward J. Ramirez, M.D., FACOG
Executive Medical Director
The Fertility and Gynecology Center
Monterey Bay IVF Program
www.montereybayivf.com

Monterey, California, U.S.A.

for additional information check out my blog at http://womenshealthandfertility.blogspot.com check me out on twitter with me at @montereybayivf and facebook @montereybayivf